ESP8266 MQTT reconnect permanently fails after internet outage until full reboot (ThingsBoard Arduino SDK)

[arimukhlas]

I'm using ESP8266 with ThingsBoard Arduino SDK and MQTT over WiFiClient.

My setup:

WiFiClient *espClient = nullptr;
ThingsBoard *tb = nullptr;

and I recreate the client dynamically:

void initThingsBoardClient() {
  if (tb != nullptr) {
    tb->disconnect();
    delete tb;
    tb = nullptr;
  }

  if (espClient != nullptr) {
    espClient->flush();
    espClient->stop();
    delete espClient;
    espClient = nullptr;
  }

  espClient = new WiFiClient();
  tb = new ThingsBoard(*espClient, MAX_MESSAGE_SIZE);
}

The device behavior is:

1. ESP8266 boots normally
2. WiFi connects
3. ThingsBoard MQTT connects successfully
4. Telemetry works correctly for hours

Then I simulate internet outage:

• Router WiFi remains connected ("WL_CONNECTED")
• But internet access is removed

During outage:

• MQTT connection fails as expected
• Pending telemetry is stored locally in LittleFS
• NTP resync fails as expected

When internet access is restored:

• Internet check becomes OK again
• NTP resync works successfully
• But MQTT connection to ThingsBoard keeps failing forever

Debug example:

[NET] Internet status = OK
[NET] Internet restored, recreate TB client
[TB] Client recreated
[NTP] Resync OK
Connecting TB : iot.pdam-sby.go.id : 1883
[TB] Connecting to server failed
TB connect failed

This repeats forever.

Important:

• WiFi remains connected
• DNS works
• NTP works again after internet restore
• Only ThingsBoard MQTT reconnect fails
• Restarting ESP8266 immediately fixes everything
• After restart, ThingsBoard reconnects successfully and all pending telemetry is sent

I already tried:

• "tb.disconnect()"
• "espClient.flush()"
• "espClient.stop()"
• recreating "WiFiClient"
• recreating "ThingsBoard"
• WiFi reconnect
• WiFi.mode(WIFI_OFF)
• recreating MQTT objects dynamically

But MQTT reconnect still fails until full ESP restart.

Questions:

1. Is this a known PubSubClient / ThingsBoard SDK issue on ESP8266?
2. Is there any internal MQTT state that survives object recreation?
3. Is there a recommended full MQTT reset procedure without rebooting ESP?
4. Could repeated failed reconnect attempts after internet outage cause internal socket lockup?
5. Is there a safer reconnect flow recommended by the SDK maintainers?

Thank you.

[arimukhlas]

hi @MathewHDYT , @imbeacon sorry if I tagged you
please help, give me a hint, thank you so much