diff --git a/Adjust.podspec b/Adjust.podspec
index 9b0fa6970..316a436b0 100644
--- a/Adjust.podspec
+++ b/Adjust.podspec
@@ -1,11 +1,11 @@
 Pod::Spec.new do |s|
   s.name           = "Adjust"
-  s.version        = "4.21.2"
+  s.version        = "4.21.3"
   s.summary        = "This is the iOS SDK of adjust. You can read more about it at http://adjust.com."
   s.homepage       = "https://github.com/adjust/ios_sdk"
   s.license        = { :type => 'MIT', :file => 'MIT-LICENSE' }
   s.author         = { "Christian Wellenbrock" => "welle@adjust.com" }
-  s.source         = { :git => "https://github.com/adjust/ios_sdk.git", :tag => "v4.21.2" }
+  s.source         = { :git => "https://github.com/adjust/ios_sdk.git", :tag => "v4.21.3" }
   s.ios.deployment_target = '6.0'
   s.tvos.deployment_target = '9.0'
   s.framework      = 'SystemConfiguration'
diff --git a/Adjust/ADJActivityHandler.m b/Adjust/ADJActivityHandler.m
index d6f1c4697..6f8311c21 100644
--- a/Adjust/ADJActivityHandler.m
+++ b/Adjust/ADJActivityHandler.m
@@ -32,7 +32,6 @@
 static NSString   * const kForegroundTimerName   = @"Foreground timer";
 static NSString   * const kBackgroundTimerName   = @"Background timer";
 static NSString   * const kDelayStartTimerName   = @"Delay Start timer";
-static NSString   * const kiAdTimeoutTimerName   = @"iAd Timeout timer";
 
 static NSTimeInterval kForegroundTimerInterval;
 static NSTimeInterval kForegroundTimerStart;
@@ -87,7 +86,6 @@ @interface ADJActivityHandler()
 @property (nonatomic, strong) ADJActivityState *activityState;
 @property (nonatomic, strong) ADJTimerCycle *foregroundTimer;
 @property (nonatomic, strong) ADJTimerOnce *backgroundTimer;
-@property (nonatomic, strong) ADJTimerOnce *iAdTimeoutTimer;
 @property (nonatomic, assign) NSInteger iAdRetriesLeft;
 @property (nonatomic, strong) ADJInternalState *internalState;
 @property (nonatomic, strong) ADJDeviceInfo *deviceInfo;
@@ -110,7 +108,6 @@ typedef NS_ENUM(NSInteger, AdjADClientError) {
     AdjADClientErrorLimitAdTracking = 1,
     AdjADClientErrorMissingData = 2,
     AdjADClientErrorCorruptResponse = 3,
-    AdjCustomErrorTimeout = 100,
 };
 
 #pragma mark -
@@ -400,9 +397,6 @@ - (void)setTrackingStateOptedOut {
 - (void)setAttributionDetails:(NSDictionary *)attributionDetails
                         error:(NSError *)error
 {
-    if (self.iAdTimeoutTimer) {
-        [self.iAdTimeoutTimer cancel];
-    }
     if (![ADJUtil isNull:error]) {
         [self.logger warn:@"Unable to read iAd details"];
 
@@ -415,7 +409,6 @@ - (void)setAttributionDetails:(NSDictionary *)attributionDetails
         //      - AdjADClientErrorUnknown
         //      - AdjADClientErrorMissingData
         //      - AdjADClientErrorCorruptResponse
-        //      - AdjCustomErrorTimeout
         // apply following retry logic:
         //      - 1st retry after 5 seconds
         //      - 2nd retry after 2 seconds
@@ -423,8 +416,7 @@ - (void)setAttributionDetails:(NSDictionary *)attributionDetails
         switch (error.code) {
             case AdjADClientErrorUnknown:
             case AdjADClientErrorMissingData:
-            case AdjADClientErrorCorruptResponse:
-            case AdjCustomErrorTimeout: {
+            case AdjADClientErrorCorruptResponse: {
                 int64_t iAdRetryDelay = 0;
                 switch (self.iAdRetriesLeft) {
                     case 2:
@@ -638,9 +630,6 @@ - (void)teardown
     if (self.backgroundTimer != nil) {
         [self.backgroundTimer cancel];
     }
-    if (self.iAdTimeoutTimer != nil) {
-        [self.iAdTimeoutTimer cancel];
-    }
     if (self.foregroundTimer != nil) {
         [self.foregroundTimer cancel];
     }
@@ -668,7 +657,6 @@ - (void)teardown
     self.sdkClickHandler = nil;
     self.foregroundTimer = nil;
     self.backgroundTimer = nil;
-    self.iAdTimeoutTimer = nil;
     self.adjustDelegate = nil;
     self.adjustConfig = nil;
     self.internalState = nil;
@@ -1320,21 +1308,7 @@ - (void)checkForiAd {
 }
 
 - (void)checkForiAdI:(ADJActivityHandler *)selfI {
-    if (selfI.iAdTimeoutTimer == nil) {
-        selfI.iAdTimeoutTimer =
-            [ADJTimerOnce
-                timerWithBlock:^{
-                [selfI setAttributionDetails:nil
-                                      error:[NSError errorWithDomain:@"com.adjust.sdk.iAd"
-                                                                code:100
-                                                            userInfo:@{@"Error reason": @"iAd request timed out"}]];
-
-            }
-             queue:selfI.internalQueue
-             name:kiAdTimeoutTimerName];
-    }
-
-    [[UIDevice currentDevice] adjCheckForiAd:selfI iAdTimeoutTimer:selfI.iAdTimeoutTimer];
+    [[UIDevice currentDevice] adjCheckForiAd:selfI];
 }
 
 - (void)setOfflineModeI:(ADJActivityHandler *)selfI
@@ -1446,7 +1420,7 @@ - (void)appWillOpenUrlI:(ADJActivityHandler *)selfI
                                                                              config:selfI.adjustConfig
                                                                   sessionParameters:selfI.sessionParameters
                                                                           createdAt:now];
-    clickBuilder.deeplinkParameters = adjustDeepLinks;
+    clickBuilder.deeplinkParameters = [adjustDeepLinks copy];
     clickBuilder.attribution = deeplinkAttribution;
     clickBuilder.clickTime = clickTime;
     clickBuilder.deeplink = [url absoluteString];
diff --git a/Adjust/ADJAdditions/UIDevice+ADJAdditions.h b/Adjust/ADJAdditions/UIDevice+ADJAdditions.h
index 4bba1d86e..b1778204d 100644
--- a/Adjust/ADJAdditions/UIDevice+ADJAdditions.h
+++ b/Adjust/ADJAdditions/UIDevice+ADJAdditions.h
@@ -20,6 +20,5 @@
 - (NSString *)adjDeviceName;
 - (NSString *)adjCreateUuid;
 - (NSString *)adjVendorId;
-- (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler
-       iAdTimeoutTimer:(ADJTimerOnce *)iAdTimeoutTimer;
+- (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler;
 @end
diff --git a/Adjust/ADJAdditions/UIDevice+ADJAdditions.m b/Adjust/ADJAdditions/UIDevice+ADJAdditions.m
index 7f10cc173..b62da6d2f 100644
--- a/Adjust/ADJAdditions/UIDevice+ADJAdditions.m
+++ b/Adjust/ADJAdditions/UIDevice+ADJAdditions.m
@@ -158,9 +158,7 @@ - (NSString *)adjVendorId {
     return @"";
 }
 
-- (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler
-       iAdTimeoutTimer:(ADJTimerOnce *)iAdTimeoutTimer
-{
+- (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler {
     // if no tries for iad v3 left, stop trying
     id<ADJLogger> logger = [ADJAdjustFactory logger];
 
@@ -192,8 +190,7 @@ - (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler
     [logger debug:@"iAd framework successfully found in user's app"];
 
     BOOL iAdInformationAvailable = [self setiAdWithDetails:activityHandler
-                                   adcClientSharedInstance:ADClientSharedClientInstance
-                                           iAdTimeoutTimer:iAdTimeoutTimer];
+                                   adcClientSharedInstance:ADClientSharedClientInstance];
 
     if (!iAdInformationAvailable) {
         [logger warn:@"iAd information not available"];
@@ -204,9 +201,7 @@ - (void)adjCheckForiAd:(ADJActivityHandler *)activityHandler
 }
 
 - (BOOL)setiAdWithDetails:(ADJActivityHandler *)activityHandler
-  adcClientSharedInstance:(id)ADClientSharedClientInstance
-          iAdTimeoutTimer:(ADJTimerOnce *)iAdTimeoutTimer
-{
+  adcClientSharedInstance:(id)ADClientSharedClientInstance {
     SEL iAdDetailsSelector = NSSelectorFromString(@"requestAttributionDetailsWithBlock:");
     if (![ADClientSharedClientInstance respondsToSelector:iAdDetailsSelector]) {
         return NO;
@@ -220,9 +215,6 @@ - (BOOL)setiAdWithDetails:(ADJActivityHandler *)activityHandler
                                                                             error:error];
                                        }];
 #pragma clang diagnostic pop
-    if (iAdTimeoutTimer) {
-        [iAdTimeoutTimer startIn:5.0];
-    }
     return YES;
 }
 
diff --git a/Adjust/ADJEvent.m b/Adjust/ADJEvent.m
index 87132abb1..ecb6b1cd8 100644
--- a/Adjust/ADJEvent.m
+++ b/Adjust/ADJEvent.m
@@ -10,11 +10,12 @@
 #import "ADJAdjustFactory.h"
 #import "ADJUtil.h"
 
-#pragma mark -
 @interface ADJEvent()
+
 @property (nonatomic, weak) id<ADJLogger> logger;
-@property (nonatomic, strong) NSMutableDictionary* callbackMutableParameters;
-@property (nonatomic, strong) NSMutableDictionary* partnerMutableParameters;
+@property (nonatomic, strong) NSMutableDictionary *callbackMutableParameters;
+@property (nonatomic, strong) NSMutableDictionary *partnerMutableParameters;
+
 @end
 
 @implementation ADJEvent
@@ -23,86 +24,109 @@ + (ADJEvent *)eventWithEventToken:(NSString *)eventToken {
     return [[ADJEvent alloc] initWithEventToken:eventToken];
 }
 
-- (id) initWithEventToken:(NSString *)eventToken {
+- (id)initWithEventToken:(NSString *)eventToken {
     self = [super init];
-    if (self == nil) return nil;
+    if (self == nil) {
+        return nil;
+    }
 
     self.logger = ADJAdjustFactory.logger;
 
-    if (![self checkEventToken:eventToken]) return self;
+    if (![self checkEventToken:eventToken]) {
+        return self;
+    }
 
-    _eventToken = eventToken;
+    _eventToken = [eventToken copy];
 
     return self;
 }
 
-- (void) addCallbackParameter:(NSString *)key
-                        value:(NSString *)value
-{
-    if (![ADJUtil isValidParameter:key
-                     attributeType:@"key"
-                     parameterName:@"Callback"]) return;
+- (void)addCallbackParameter:(NSString *)key value:(NSString *)value {
+    @synchronized (self) {
+        NSString *immutableKey = [key copy];
+        NSString *immutableValue = [value copy];
 
-    if (![ADJUtil isValidParameter:value
-                     attributeType:@"value"
-                     parameterName:@"Callback"]) return;
-
-    if (self.callbackMutableParameters == nil) {
-        self.callbackMutableParameters = [[NSMutableDictionary alloc] init];
-    }
+        if (![ADJUtil isValidParameter:immutableKey
+                         attributeType:@"key"
+                         parameterName:@"Callback"]) {
+            return;
+        }
+        if (![ADJUtil isValidParameter:immutableValue
+                         attributeType:@"value"
+                         parameterName:@"Callback"]) {
+            return;
+        }
 
-    if ([self.callbackMutableParameters objectForKey:key]) {
-        [self.logger warn:@"key %@ was overwritten", key];
+        if (self.callbackMutableParameters == nil) {
+            self.callbackMutableParameters = [[NSMutableDictionary alloc] init];
+        }
+        if ([self.callbackMutableParameters objectForKey:immutableKey]) {
+            [self.logger warn:@"Callback parameter key %@ was overwritten", immutableKey];
+        }
+        [self.callbackMutableParameters setObject:immutableValue forKey:immutableKey];
     }
-
-    [self.callbackMutableParameters setObject:value forKey:key];
 }
 
-- (void) addPartnerParameter:(NSString *)key
-                       value:(NSString *)value {
-
-    if (![ADJUtil isValidParameter:key
-                     attributeType:@"key"
-                     parameterName:@"Partner"]) return;
+- (void)addPartnerParameter:(NSString *)key value:(NSString *)value {
+    @synchronized (self) {
+        NSString *immutableKey = [key copy];
+        NSString *immutableValue = [value copy];
 
-    if (![ADJUtil isValidParameter:value
-                     attributeType:@"value"
-                     parameterName:@"Partner"]) return;
-
-    if (self.partnerMutableParameters == nil) {
-        self.partnerMutableParameters = [[NSMutableDictionary alloc] init];
-    }
+        if (![ADJUtil isValidParameter:immutableKey
+                         attributeType:@"key"
+                         parameterName:@"Partner"]) {
+            return;
+        }
+        if (![ADJUtil isValidParameter:immutableValue
+                         attributeType:@"value"
+                         parameterName:@"Partner"]) {
+            return;
+        }
 
-    if ([self.partnerMutableParameters objectForKey:key]) {
-        [self.logger warn:@"key %@ was overwritten", key];
+        if (self.partnerMutableParameters == nil) {
+            self.partnerMutableParameters = [[NSMutableDictionary alloc] init];
+        }
+        if ([self.partnerMutableParameters objectForKey:immutableKey]) {
+            [self.logger warn:@"Partner parameter key %@ was overwritten", immutableKey];
+        }
+        [self.partnerMutableParameters setObject:immutableValue forKey:immutableKey];
     }
-
-    [self.partnerMutableParameters setObject:value forKey:key];
 }
 
-- (void) setRevenue:(double) amount currency:(NSString *)currency{
-    NSNumber * revenue = [NSNumber numberWithDouble:amount];
-
-    if (![self checkRevenue:revenue currency:currency]) return;
+- (void)setRevenue:(double)amount currency:(NSString *)currency {
+    NSNumber *revenue = [NSNumber numberWithDouble:amount];
+    if (![self checkRevenue:revenue currency:currency]) {
+        return;
+    }
 
     _revenue = revenue;
-    _currency = currency;
+    @synchronized (self) {
+        _currency = [currency copy];
+    }
 }
 
-- (void) setTransactionId:(NSString *)transactionId {
-    _transactionId = transactionId;
+- (void)setTransactionId:(NSString *)transactionId {
+    @synchronized (self) {
+        _transactionId = [transactionId copy];
+    }
 }
 
 - (void)setCallbackId:(NSString *)callbackId {
-    _callbackId = callbackId;
+    @synchronized (self) {
+        _callbackId = [callbackId copy];
+    }
 }
 
-- (NSDictionary *) callbackParameters {
-    return (NSDictionary *) self.callbackMutableParameters;
+- (NSDictionary *)callbackParameters {
+    @synchronized (self) {
+        return (NSDictionary *)self.callbackMutableParameters;
+    }
 }
 
-- (NSDictionary *) partnerParameters {
-    return (NSDictionary *) self.partnerMutableParameters;
+- (NSDictionary *)partnerParameters {
+    @synchronized (self) {
+        return (NSDictionary *)self.partnerMutableParameters;
+    }
 }
 
 - (BOOL)checkEventToken:(NSString *)eventToken {
@@ -117,21 +141,17 @@ - (BOOL)checkEventToken:(NSString *)eventToken {
     return YES;
 }
 
-- (BOOL) checkRevenue:(NSNumber*) revenue
-             currency:(NSString*) currency
-{
+- (BOOL)checkRevenue:(NSNumber *)revenue currency:(NSString *)currency {
     if (![ADJUtil isNull:revenue]) {
         double amount =  [revenue doubleValue];
         if (amount < 0.0) {
             [self.logger error:@"Invalid amount %.5f", amount];
             return NO;
         }
-
         if ([ADJUtil isNull:currency]) {
             [self.logger error:@"Currency must be set with revenue"];
             return NO;
         }
-
         if ([currency isEqualToString:@""]) {
             [self.logger error:@"Currency is empty"];
             return NO;
@@ -146,12 +166,14 @@ - (BOOL) checkRevenue:(NSNumber*) revenue
     return YES;
 }
 
-- (BOOL) isValid {
+- (BOOL)isValid {
     return self.eventToken != nil;
 }
 
-- (void) setReceipt:(NSData *)receipt transactionId:(NSString *)transactionId {
-    if (![self checkReceipt:receipt transactionId:transactionId]) return;
+- (void)setReceipt:(NSData *)receipt transactionId:(NSString *)transactionId {
+    if (![self checkReceipt:receipt transactionId:transactionId]) {
+        return;
+    }
 
     if ([ADJUtil isNull:receipt] || [receipt length] == 0) {
         _emptyReceipt = YES;
@@ -160,7 +182,7 @@ - (void) setReceipt:(NSData *)receipt transactionId:(NSString *)transactionId {
     _transactionId = transactionId;
 }
 
-- (BOOL) checkReceipt:(NSData *)receipt transactionId:(NSString *)transactionId {
+- (BOOL)checkReceipt:(NSData *)receipt transactionId:(NSString *)transactionId {
     if ([ADJUtil isNotNull:receipt] && [ADJUtil isNull:transactionId]) {
         [self.logger error:@"Missing transactionId"];
         return NO;
@@ -168,9 +190,9 @@ - (BOOL) checkReceipt:(NSData *)receipt transactionId:(NSString *)transactionId
     return YES;
 }
 
--(id)copyWithZone:(NSZone *)zone
-{
-    ADJEvent* copy = [[[self class] allocWithZone:zone] init];
+- (id)copyWithZone:(NSZone *)zone {
+    ADJEvent *copy = [[[self class] allocWithZone:zone] init];
+
     if (copy) {
         copy->_eventToken = [self.eventToken copyWithZone:zone];
         copy->_revenue = [self.revenue copyWithZone:zone];
@@ -181,6 +203,7 @@ -(id)copyWithZone:(NSZone *)zone
         copy->_receipt = [self.receipt copyWithZone:zone];
         copy->_emptyReceipt = self.emptyReceipt;
     }
+
     return copy;
 }
 
diff --git a/Adjust/ADJPackageBuilder.m b/Adjust/ADJPackageBuilder.m
index c3f927521..6d67f92dc 100644
--- a/Adjust/ADJPackageBuilder.m
+++ b/Adjust/ADJPackageBuilder.m
@@ -299,8 +299,8 @@ - (NSMutableDictionary *)getSessionParameters:(BOOL)isInDelay {
     }
 
     if (!isInDelay) {
-        [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.callbackParameters forKey:@"callback_params"];
-        [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.partnerParameters forKey:@"partner_params"];
+        [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.callbackParameters copy] forKey:@"callback_params"];
+        [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.partnerParameters copy] forKey:@"partner_params"];
     }
 
 #if !TARGET_OS_TV && !TARGET_OS_MACCATALYST
@@ -368,11 +368,11 @@ - (NSMutableDictionary *)getEventParameters:(BOOL)isInDelay forEventPackage:(ADJ
     }
 
     if (!isInDelay) {
-        NSDictionary *mergedCallbackParameters = [ADJUtil mergeParameters:self.sessionParameters.callbackParameters
-                                                                   source:event.callbackParameters
+        NSDictionary *mergedCallbackParameters = [ADJUtil mergeParameters:[self.sessionParameters.callbackParameters copy]
+                                                                   source:[event.callbackParameters copy]
                                                             parameterName:@"Callback"];
-        NSDictionary *mergedPartnerParameters = [ADJUtil mergeParameters:self.sessionParameters.partnerParameters
-                                                                  source:event.partnerParameters
+        NSDictionary *mergedPartnerParameters = [ADJUtil mergeParameters:[self.sessionParameters.partnerParameters copy]
+                                                                  source:[event.partnerParameters copy]
                                                            parameterName:@"Partner"];
 
         [ADJPackageBuilder parameters:parameters setDictionary:mergedCallbackParameters forKey:@"callback_params"];
@@ -507,7 +507,7 @@ - (NSMutableDictionary *)getClickParameters:(NSString *)source {
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.bundleShortVersion forKey:@"app_version_short"];
     [ADJPackageBuilder parameters:parameters setBool:YES forKey:@"attribution_deeplink"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.bundeIdentifier forKey:@"bundle_id"];
-    [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.callbackParameters forKey:@"callback_params"];
+    [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.callbackParameters copy] forKey:@"callback_params"];
     [ADJPackageBuilder parameters:parameters setDate:self.clickTime forKey:@"click_time"];
     [ADJPackageBuilder parameters:parameters setNumberInt:[ADJUtil readReachabilityFlags] forKey:@"connectivity_type"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.countryCode forKey:@"country"];
@@ -535,7 +535,7 @@ - (NSMutableDictionary *)getClickParameters:(NSString *)source {
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.osName forKey:@"os_name"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.systemVersion forKey:@"os_version"];
     [ADJPackageBuilder parameters:parameters setDictionary:self.deeplinkParameters forKey:@"params"];
-    [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.partnerParameters forKey:@"partner_params"];
+    [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.partnerParameters copy] forKey:@"partner_params"];
     [ADJPackageBuilder parameters:parameters setDate:self.purchaseTime forKey:@"purchase_time"];
     [ADJPackageBuilder parameters:parameters setString:self.adjustConfig.secretId forKey:@"secret_id"];
     [ADJPackageBuilder parameters:parameters setString:source forKey:@"source"];
@@ -666,7 +666,7 @@ - (NSMutableDictionary *)getDisableThirdPartySharingParameters {
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.bundleShortVersion forKey:@"app_version_short"];
     [ADJPackageBuilder parameters:parameters setBool:YES forKey:@"attribution_deeplink"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.bundeIdentifier forKey:@"bundle_id"];
-    [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.callbackParameters forKey:@"callback_params"];
+    [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.callbackParameters copy] forKey:@"callback_params"];
     [ADJPackageBuilder parameters:parameters setDate:self.clickTime forKey:@"click_time"];
     [ADJPackageBuilder parameters:parameters setNumberInt:[ADJUtil readReachabilityFlags] forKey:@"connectivity_type"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.countryCode forKey:@"country"];
@@ -694,7 +694,7 @@ - (NSMutableDictionary *)getDisableThirdPartySharingParameters {
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.osName forKey:@"os_name"];
     [ADJPackageBuilder parameters:parameters setString:self.deviceInfo.systemVersion forKey:@"os_version"];
     [ADJPackageBuilder parameters:parameters setDictionary:self.deeplinkParameters forKey:@"params"];
-    [ADJPackageBuilder parameters:parameters setDictionary:self.sessionParameters.partnerParameters forKey:@"partner_params"];
+    [ADJPackageBuilder parameters:parameters setDictionary:[self.sessionParameters.partnerParameters copy] forKey:@"partner_params"];
     [ADJPackageBuilder parameters:parameters setDate:self.purchaseTime forKey:@"purchase_time"];
     [ADJPackageBuilder parameters:parameters setString:self.adjustConfig.secretId forKey:@"secret_id"];
     [ADJPackageBuilder parameters:parameters setInt:UIDevice.currentDevice.adjTrackingEnabled forKey:@"tracking_enabled"];
diff --git a/Adjust/ADJUtil.m b/Adjust/ADJUtil.m
index 6f103c499..ef867f2ed 100644
--- a/Adjust/ADJUtil.m
+++ b/Adjust/ADJUtil.m
@@ -43,7 +43,7 @@
 static CTTelephonyNetworkInfo *networkInfo = nil;
 #endif
 
-static NSString * const kClientSdk                  = @"ios4.21.2";
+static NSString * const kClientSdk                  = @"ios4.21.3";
 static NSString * const kDeeplinkParam              = @"deep_link=";
 static NSString * const kSchemeDelimiter            = @"://";
 static NSString * const kDefaultScheme              = @"AdjustUniversalScheme";
@@ -1330,7 +1330,7 @@ + (NSString *)convertDeviceToken:(NSData *)deviceToken {
         [hexString appendString:[NSString stringWithFormat:@"%02lx", (unsigned long)dataBuffer[i]]];
     }
 
-    return [NSString stringWithString:hexString];
+    return [hexString copy];
 }
 
 + (BOOL)checkAttributionDetails:(NSDictionary *)attributionDetails {
diff --git a/Adjust/Adjust.h b/Adjust/Adjust.h
index f33bbc0eb..6e9c5ad79 100644
--- a/Adjust/Adjust.h
+++ b/Adjust/Adjust.h
@@ -2,7 +2,7 @@
 //  Adjust.h
 //  Adjust
 //
-//  V4.21.2
+//  V4.21.3
 //  Created by Christian Wellenbrock (wellle) on 23rd July 2013.
 //  Copyright © 2012-2017 Adjust GmbH. All rights reserved.
 //
diff --git a/Adjust/Adjust.m b/Adjust/Adjust.m
index 0e0d01042..228d5615f 100644
--- a/Adjust/Adjust.m
+++ b/Adjust/Adjust.m
@@ -85,44 +85,64 @@ - (id)init {
 #pragma mark - Public static methods
 
 + (void)appDidLaunch:(ADJConfig *)adjustConfig {
-    [[Adjust getInstance] appDidLaunch:adjustConfig];
+    @synchronized (self) {
+        [[Adjust getInstance] appDidLaunch:adjustConfig];
+    }
 }
 
 + (void)trackEvent:(ADJEvent *)event {
-    [[Adjust getInstance] trackEvent:event];
+    @synchronized (self) {
+        [[Adjust getInstance] trackEvent:event];
+    }
 }
 
 + (void)trackSubsessionStart {
-    [[Adjust getInstance] trackSubsessionStart];
+    @synchronized (self) {
+        [[Adjust getInstance] trackSubsessionStart];
+    }
 }
 
 + (void)trackSubsessionEnd {
-    [[Adjust getInstance] trackSubsessionEnd];
+    @synchronized (self) {
+        [[Adjust getInstance] trackSubsessionEnd];
+    }
 }
 
 + (void)setEnabled:(BOOL)enabled {
-    Adjust *instance = [Adjust getInstance];
-    [instance setEnabled:enabled];
+    @synchronized (self) {
+        Adjust *instance = [Adjust getInstance];
+        [instance setEnabled:enabled];
+    }
 }
 
 + (BOOL)isEnabled {
-    return [[Adjust getInstance] isEnabled];
+    @synchronized (self) {
+        return [[Adjust getInstance] isEnabled];
+    }
 }
 
 + (void)appWillOpenUrl:(NSURL *)url {
-    [[Adjust getInstance] appWillOpenUrl:url];
+    @synchronized (self) {
+        [[Adjust getInstance] appWillOpenUrl:[url copy]];
+    }
 }
 
 + (void)setDeviceToken:(NSData *)deviceToken {
-    [[Adjust getInstance] setDeviceToken:deviceToken];
+    @synchronized (self) {
+        [[Adjust getInstance] setDeviceToken:[deviceToken copy]];
+    }
 }
 
 + (void)setPushToken:(NSString *)pushToken {
-    [[Adjust getInstance] setPushToken:pushToken];
+    @synchronized (self) {
+        [[Adjust getInstance] setPushToken:[pushToken copy]];
+    }
 }
 
 + (void)setOfflineMode:(BOOL)enabled {
-    [[Adjust getInstance] setOfflineMode:enabled];
+    @synchronized (self) {
+        [[Adjust getInstance] setOfflineMode:enabled];
+    }
 }
 
 + (void)sendAdWordsRequest {
@@ -130,77 +150,107 @@ + (void)sendAdWordsRequest {
 }
 
 + (NSString *)idfa {
-    return [[Adjust getInstance] idfa];
+    @synchronized (self) {
+        return [[Adjust getInstance] idfa];
+    }
 }
 
 + (NSString *)sdkVersion {
-    return [[Adjust getInstance] sdkVersion];
+    @synchronized (self) {
+        return [[Adjust getInstance] sdkVersion];
+    }
 }
 
 + (NSURL *)convertUniversalLink:(NSURL *)url scheme:(NSString *)scheme {
-    return [[Adjust getInstance] convertUniversalLink:url scheme:scheme];
+    @synchronized (self) {
+        return [[Adjust getInstance] convertUniversalLink:[url copy] scheme:[scheme copy]];
+    }
 }
 
 + (void)sendFirstPackages {
-    [[Adjust getInstance] sendFirstPackages];
+    @synchronized (self) {
+        [[Adjust getInstance] sendFirstPackages];
+    }
 }
 
 + (void)addSessionCallbackParameter:(NSString *)key value:(NSString *)value {
-    [[Adjust getInstance] addSessionCallbackParameter:key value:value];
-
+    @synchronized (self) {
+        [[Adjust getInstance] addSessionCallbackParameter:[key copy] value:[value copy]];
+    }
 }
 
 + (void)addSessionPartnerParameter:(NSString *)key value:(NSString *)value {
-    [[Adjust getInstance] addSessionPartnerParameter:key value:value];
+    @synchronized (self) {
+        [[Adjust getInstance] addSessionPartnerParameter:[key copy] value:[value copy]];
+    }
 }
 
-
 + (void)removeSessionCallbackParameter:(NSString *)key {
-    [[Adjust getInstance] removeSessionCallbackParameter:key];
+    @synchronized (self) {
+        [[Adjust getInstance] removeSessionCallbackParameter:[key copy]];
+    }
 }
 
 + (void)removeSessionPartnerParameter:(NSString *)key {
-    [[Adjust getInstance] removeSessionPartnerParameter:key];
+    @synchronized (self) {
+        [[Adjust getInstance] removeSessionPartnerParameter:[key copy]];
+    }
 }
 
 + (void)resetSessionCallbackParameters {
-    [[Adjust getInstance] resetSessionCallbackParameters];
+    @synchronized (self) {
+        [[Adjust getInstance] resetSessionCallbackParameters];
+    }
 }
 
 + (void)resetSessionPartnerParameters {
-    [[Adjust getInstance] resetSessionPartnerParameters];
+    @synchronized (self) {
+        [[Adjust getInstance] resetSessionPartnerParameters];
+    }
 }
 
 + (void)gdprForgetMe {
-    [[Adjust getInstance] gdprForgetMe];
+    @synchronized (self) {
+        [[Adjust getInstance] gdprForgetMe];
+    }
 }
 
 + (void)trackAdRevenue:(nonnull NSString *)source payload:(nonnull NSData *)payload {
-    [[Adjust getInstance] trackAdRevenue:source payload:payload];
+    @synchronized (self) {
+        [[Adjust getInstance] trackAdRevenue:[source copy] payload:[payload copy]];
+    }
 }
 
 + (void)disableThirdPartySharing {
-    [[Adjust getInstance] disableThirdPartySharing];
+    @synchronized (self) {
+        [[Adjust getInstance] disableThirdPartySharing];
+    }
 }
 
 + (ADJAttribution *)attribution {
-    return [[Adjust getInstance] attribution];
+    @synchronized (self) {
+        return [[Adjust getInstance] attribution];
+    }
 }
 
 + (NSString *)adid {
-    return [[Adjust getInstance] adid];
+    @synchronized (self) {
+        return [[Adjust getInstance] adid];
+    }
 }
 
 + (void)setTestOptions:(AdjustTestOptions *)testOptions {
-    if (testOptions.teardown) {
-        if (defaultInstance != nil) {
-            [defaultInstance teardown];
+    @synchronized (self) {
+        if (testOptions.teardown) {
+            if (defaultInstance != nil) {
+                [defaultInstance teardown];
+            }
+            defaultInstance = nil;
+            onceToken = 0;
+            [ADJAdjustFactory teardown:testOptions.deleteState];
         }
-        defaultInstance = nil;
-        onceToken = 0;
-        [ADJAdjustFactory teardown:testOptions.deleteState];
+        [[Adjust getInstance] setTestOptions:(AdjustTestOptions *)testOptions];
     }
-    [[Adjust getInstance] setTestOptions:(AdjustTestOptions *)testOptions];
 }
 
 #pragma mark - Public instance methods
diff --git a/AdjustBridge/AdjustBridgeRegister.m b/AdjustBridge/AdjustBridgeRegister.m
index 8ae4c40cf..b87799a2d 100644
--- a/AdjustBridge/AdjustBridgeRegister.m
+++ b/AdjustBridge/AdjustBridgeRegister.m
@@ -221,7 +221,7 @@ + (NSString *)adjust_js {
                 if (this.sdkPrefix) {
                     return this.sdkPrefix;
                 } else {
-                    return 'web-bridge4.21.2';
+                    return 'web-bridge4.21.3';
                 }
             },
             setTestOptions: function(testOptions) {
diff --git a/AdjustTests/AdjustUnitTests/ADJPackageFields.m b/AdjustTests/AdjustUnitTests/ADJPackageFields.m
index 13606d9e9..ab7a0b56e 100644
--- a/AdjustTests/AdjustUnitTests/ADJPackageFields.m
+++ b/AdjustTests/AdjustUnitTests/ADJPackageFields.m
@@ -16,7 +16,7 @@ - (id) init {
 
     // default values
     self.appToken = @"qwerty123456";
-    self.clientSdk = @"ios4.21.2";
+    self.clientSdk = @"ios4.21.3";
     self.suffix = @"";
     self.environment = @"sandbox";
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index cd92d282e..3251a15ce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,15 @@
+### Version 4.21.3 (22nd April 2020)
+#### Changed
+- Added copying of each injected mutable property of `ADJEvent` class.
+- Synchronised access to callback/partner parameters in `ADJEvent` class.
+- Synchronised access to public API methods in `Adjust` class.
+
+#### Fixed
+- Removed iAd timer.
+- Removed activity package mutation scenarios after package has been created.
+
+---
+
 ### Version 4.21.2 (15th April 2020)
 #### Fixed
 - Added check for timer source and block existence prior to starting it.
diff --git a/README.md b/README.md
index 30bff553e..e2ade75b1 100644
--- a/README.md
+++ b/README.md
@@ -74,13 +74,13 @@ We will describe the steps to integrate the Adjust SDK into your iOS project. We
 If you're using [CocoaPods][cocoapods], you can add the following line to your `Podfile` and continue from [this step](#sdk-integrate):
 
 ```ruby
-pod 'Adjust', '~> 4.21.2'
+pod 'Adjust', '~> 4.21.3'
 ```
 
 or:
 
 ```ruby
-pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.2'
+pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.3'
 ```
 
 ---
diff --git a/VERSION b/VERSION
index c93e58ee0..fedb11348 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.21.2
+4.21.3
diff --git a/doc/chinese/README.md b/doc/chinese/README.md
index 1acf5ab24..4d497188b 100644
--- a/doc/chinese/README.md
+++ b/doc/chinese/README.md
@@ -73,13 +73,13 @@ Read this in other languages: [English][en-readme], [中文][zh-readme], [日本
 如果您正在使用[CocoaPods][cocoapods],您可以将以下代码行添加至 `Podfile`，然后继续进行[此步骤](#sdk-integrate):
 
 ```ruby
-pod 'Adjust', '~> 4.21.2'
+pod 'Adjust', '~> 4.21.3'
 ```
 
 或:
 
 ```ruby
-pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.2'
+pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.3'
 ```
 
 ---
diff --git a/doc/english/migrate.md b/doc/english/migrate.md
index e74db1313..754f75536 100644
--- a/doc/english/migrate.md
+++ b/doc/english/migrate.md
@@ -1,4 +1,4 @@
-## Migrate your Adjust SDK for iOS to v4.21.2 from v3.4.0
+## Migrate your Adjust SDK for iOS to v4.21.3 from v3.4.0
 
 ### Initial setup
 
diff --git a/doc/english/web_views.md b/doc/english/web_views.md
index 30ea2d10a..3758dc7f3 100644
--- a/doc/english/web_views.md
+++ b/doc/english/web_views.md
@@ -64,7 +64,7 @@ We will describe the steps to integrate the Adjust SDK into your iOS project. We
 If you're using [CocoaPods][cocoapods], you can add the following line to your `Podfile` and continue from [this step](#sdk-integrate):
 
 ```ruby
-pod 'Adjust/WebBridge', '~> 4.21.2'
+pod 'Adjust/WebBridge', '~> 4.21.3'
 ```
 
 ---
diff --git a/doc/japanese/README.md b/doc/japanese/README.md
index 783d31f04..068d4cc50 100644
--- a/doc/japanese/README.md
+++ b/doc/japanese/README.md
@@ -25,13 +25,13 @@ adjust SDKをiOSプロジェクトに連携する手順を説明します。
 [こちらの手順](#sdk-integrate)に進んでください。
 
 ```ruby
-pod 'Adjust', '~> 4.21.2'
+pod 'Adjust', '~> 4.21.3'
 ```
 
 または
 
 ```ruby
-pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.2'
+pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.3'
 ```
 
 ---
diff --git a/doc/korean/README.md b/doc/korean/README.md
index c4d1678aa..98586b073 100644
--- a/doc/korean/README.md
+++ b/doc/korean/README.md
@@ -73,13 +73,13 @@ iOS 개발용 Xcode를 사용한다는 가정하에 iOS 프로젝트에 Adjust S
 [CocoaPods][cocoapods]를 사용하는 경우, 다음 내용을 `Podfile`에 추가한 후 [해당 단계](#sdk-integrate)를 완료하세요.
 
 ```ruby
-pod 'Adjust', '~> 4.21.2'
+pod 'Adjust', '~> 4.21.3'
 ```
 
 또는:
 
 ```ruby
-pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.2'
+pod 'Adjust', :git => 'https://github.com/adjust/ios_sdk.git', :tag => 'v4.21.3'
 ```
 
 ---
diff --git a/doc/korean/web_views.md b/doc/korean/web_views.md
index 1f3a32e69..e191eb289 100644
--- a/doc/korean/web_views.md
+++ b/doc/korean/web_views.md
@@ -64,7 +64,7 @@ iOS 개발용 Xcode를 사용한다는 가정하에 iOS 프로젝트에 Adjust S
 [CocoaPods][cocoapods]를 사용하는 경우, 다음 내용을 'Podfile'에 추가한 후 [해당 단계](#sdk-integrate)를 완료하세요.
 
 ```ruby
-pod 'Adjust/WebBridge', '~> 4.21.2'
+pod 'Adjust/WebBridge', '~> 4.21.3'
 ```
 
 ---
diff --git a/doc/migrate.md b/doc/migrate.md
index e74db1313..754f75536 100644
--- a/doc/migrate.md
+++ b/doc/migrate.md
@@ -1,4 +1,4 @@
-## Migrate your Adjust SDK for iOS to v4.21.2 from v3.4.0
+## Migrate your Adjust SDK for iOS to v4.21.3 from v3.4.0
 
 ### Initial setup