Mqtt Tls on boot crash tasmota if broker is not available.

[vincenzorinaldi79]

I have an ESP32 running Tasmota 15.4.0.2.
The device boots normally, connects to Wi-Fi, starts the web server, syncs NTP, and then attempts to connect to the MQTT broker using TLS.

When the broker is unreachable (for any external reason, dns resolution, down service...) at boot, Tasmota logs a TLS connection error (-1002), the MQTT connection fails, and shortly after the device crashes with:

14:59:58.068 MQT: TLS connection error: -1002
14:59:58.068 MQT: Connect failed to xyz.domain.com:8883, rc -2. Retry in 10 sec
Guru Meditation Error: Core 1 panic'ed (LoadProhibited). Exception was unhandled.

What I also noticed is that if the broker is already unavailable after the device has fully booted, Tasmota keeps retrying MQTT normally and does not crash.
So the crash seems to happen only when the MQTT TLS connection fails during the boot sequence.

Relevant details (but also for other esp32 models)
Device: ESP32-D0WD-V3

Tasmota version: 15.4.0.2

MQTT: TLS enabled

Wi-Fi and NTP work correctly

The issue appears only when the MQTT broker is missing/unreachable at boot and after some fail going to safeboot status (I disable this when device is in place on production...but I'm not happy :-D )

Can you help me to find any kind of solution?

Many thx in advance!

[nikito7]

It fails with local IP too

[s-hadinger]

I cannot reproduce. You need to give more details about your firmware and your configuration.

[vincenzorinaldi79]

Hello,

Sure, I can reproduce this issue with these devices and versions:

board: Freenove ESP32-WROOM Board (40 pin) - ESP32-WROOM-32U (38 pin)

FW tested:

{"StatusFWR":{"Version":"15.4.0.2(32d444e-tasmota32)","BuildDateTime":"2026-05-09T11:43:13","Core":"3.3.8","SDK":"5.5.4.260407","CpuFrequency":160,"Hardware":"ESP32-D0WD-V3 v3.1","CR":"493/699"}}
{"StatusFWR":{"Version":"15.3.0(release-tasmota32)","BuildDateTime":"2026-02-19T13:57:21","Core":"3.3.7","SDK":"5.3.4.260127","CpuFrequency":160,"Hardware":"ESP32-D0WD-V3 v3.1","CR":"483/699"}}
{"StatusFWR":{"Version":"15.4.0.2(f5cafb7-tasmota32)","BuildDateTime":"2026-05-09T08:58:55","Core":"3.3.8","SDK":"5.5.4.260407","CpuFrequency":160,"Hardware":"ESP32-D0WD-V3 v3.1","CR":"492/699"}}

MQTT Conf:
{"StatusMQT":{"MqttHost":"mqtt.xxx.mywire.xxx","MqttPort":xxxx,"MqttClientMask":"esp32_04","MqttClient":"esp32_04","MqttUser":"mqtt04","MqttCount":8,"MqttTLS":1,"MAX_PACKET_SIZE":1200,"KEEPALIVE":30,"SOCKET_TIMEOUT":4}}
{"StatusMQT":{"MqttHost":"mqtt.xxx.mywire.xxx","MqttPort":xxxx,"MqttClientMask":"esp32_1","MqttClient":"esp32_1","MqttUser":"mqtt02","MqttCount":6,"MqttTLS":1,"MAX_PACKET_SIZE":1200,"KEEPALIVE":30,"SOCKET_TIMEOUT":4}}
{"StatusMQT":{"MqttHost":"mqtt.xxx.mywire.xxx","MqttPort":xxxx,"MqttClientMask":"esp32_03","MqttClient":"esp32_03","MqttUser":"mqtt03","MqttCount":7,"MqttTLS":1,"MAX_PACKET_SIZE":1200,"KEEPALIVE":30,"SOCKET_TIMEOUT":4}}

Other options & Commands to configure:

SetOption55 0
SetOption65 1
TelePeriod 60

MqttFingerprint1 00
MqttFingerprint2 00
MqttFingerprint 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00;
SetOption103 1
SetOption132 1
Restart 1

The configuration is very basic; after reboot first time Tasmota acquires the certificate automatically

No rules are configured. Wi‑Fi, MQTT, and 3 sensors are set up (2 DS18B20 and 1 ADC MQ135), but I have also tested it without sensors. .
No Matter, no Auto-conf, no KNX, no timers, no Domoticz, or anything else.

If I understand correctly, @nikito7 has also reported this issue.

Let me know if you need any other specific details.

Many thx.

[s-hadinger]

Thanks, now I can reproduce. Fix will be in CI in the coming minutes

[s-hadinger]

Fixed in #24798
Thanks for reporting

[vincenzorinaldi79]

Very nice!

I can confirm the resolution of issue, simulation is blocking tcp traffic at boot and then reopen (all work great now!):

rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:244
load:0x40078000,len:13152
ho 0 tail 12 room 4
load:0x40080400,len:2892
entry 0x40080554

00:00:00.002 HDW: ESP32-D0WD-V3 v3.1
00:00:00.038 UFS: FlashFS mounted with 304 kB free
00:00:00.051 CFG: Loaded from File, Count 259
00:00:00.099 BRY: Berry initialized, RAM used 3766 bytes
00:00:00.113 Project tasmota - esp32_02 Version 15.4.0.2(a2032b7-tasmota32)-3.3.8(2026-05-28T20:46:09)
00:00:01.000 WIF: Connecting to AP1 wpt Channel 11 BSSId E6:XX:XX:XX:XX:XX in mode HT20 as esp32-02...
00:00:03.495 WIF: Connected
00:00:03.805 HTP: Web server active on esp32-02 with IP address 10.1.1.134
09:36:48.773 MQT: Attempting connection...
09:36:58.786 MQT: TLS connection error: -1002
09:36:58.787 MQT: Connect failed to mqtt.xxxx.mywire.re:1832, rc -2. Retry in 10 sec
09:37:10.888 MQT: Attempting connection...
09:37:20.902 MQT: TLS connection error: -1002
09:37:20.903 MQT: Connect failed to mqtt.xxxx.mywire.re:1832, rc -2. Retry in 20 sec
09:37:41.769 MQT: Attempting connection...
09:37:51.776 MQT: TLS connection error: -1002
09:37:51.776 MQT: Connect failed to mqtt.xxxx.mywire.re:1832, rc -2. Retry in 30 sec
09:38:16.819 RSL: STATE = {"Time":"2026-05-29T09:38:16","Uptime":"0T00:01:33","UptimeSec":93,"Heap":105,"SleepMode":"Dynamic","Sleep":50,"LoadAvg":19,"MqttCount":0,"Berry":{"HeapUsed":4,"Objects":50},"Wifi":{"AP":1,"SSId":"wpt","BSSId":"E6:XX:XX:XX:XX:XX","Channel":11,"Mode":"HT20","RSSI":36,"Signal":-82,"LinkCount":1,"Downtime":"0T00:00:04"},"Hostname":"esp32-02","IPAddress":"10.1.1.10"}

Thank you so much for the quick resolution. I really appreciate how fast this was handled.