diff --git a/fableous-be/handlers/session.go b/fableous-be/handlers/session.go
index 39ba4feb..27bbf893 100644
--- a/fableous-be/handlers/session.go
+++ b/fableous-be/handlers/session.go
@@ -16,7 +16,7 @@ import (
 func (m *module) SessionGetAllByClassroomID(classroomID string) (sessionInfos []datatransfers.SessionInfo, err error) {
 	var sessions []models.Session
 	sessionInfos = make([]datatransfers.SessionInfo, 0)
-	if sessions, err = m.db.sessionOrmer.GetAllByClassroomID(classroomID); err == gorm.ErrRecordNotFound {
+	if sessions, err = m.db.sessionOrmer.GetAllCompletedByClassroomID(classroomID); err == gorm.ErrRecordNotFound {
 		return sessionInfos, nil
 	} else if err != nil {
 		return sessionInfos, err
diff --git a/fableous-be/handlers/websocket.go b/fableous-be/handlers/websocket.go
index f5873c0c..1094b6ce 100644
--- a/fableous-be/handlers/websocket.go
+++ b/fableous-be/handlers/websocket.go
@@ -230,7 +230,9 @@ func (m *module) HubCommandWorker(conn *websocket.Conn, sess *activeSession) (er
 			// check if CONTROL message clears a controller's canvas
 			if clearedController := message.Data.(*pb.WSMessage_Control).Control.Clear; clearedController != pb.ControllerRole_NONE {
 				_ = utils.SendMessage(sess.hubConn, message)
-				_ = utils.SendMessage(sess.controllerConn[clearedController], message)
+				if targetConn, ok := sess.controllerConn[clearedController]; ok {
+					_ = utils.SendMessage(targetConn, message)
+				}
 			}
 			// check if CONTROL message kicks a controller
 			if kickedController := message.Data.(*pb.WSMessage_Control).Control.Kick; kickedController != pb.ControllerRole_NONE {
diff --git a/fableous-be/utils/websocket.go b/fableous-be/utils/websocket.go
index ce7f2481..f5a2766e 100644
--- a/fableous-be/utils/websocket.go
+++ b/fableous-be/utils/websocket.go
@@ -3,6 +3,7 @@ package utils
 import (
 	"encoding/base64"
 	"strings"
+	"sync"
 
 	"github.com/gorilla/websocket"
 	"google.golang.org/protobuf/proto"
@@ -10,12 +11,19 @@ import (
 	pb "github.com/deco-finter/fableous/fableous-be/protos"
 )
 
+var sendMutex sync.Mutex
+
 // SendMessage sends a message to the WebSocket client.
 func SendMessage(conn *websocket.Conn, message *pb.WSMessage) (err error) {
+	if conn == nil {
+		return
+	}
 	var bytes []byte
 	if bytes, err = proto.Marshal(message); err != nil {
 		return
 	}
+	sendMutex.Lock()
+	defer sendMutex.Unlock()
 	err = conn.WriteMessage(websocket.BinaryMessage, bytes)
 	return
 }