App failed to talk to MQTT broker, but can establish TCP connection to it.

[TheHolm]

Symptoms: The app is unable to send any info to MQTT broker.

App is failing with error message as bellow. I run packed capture on the broker for non encrypted MQTT. Tcp connection get established then instantly closed by client without transmitting any data. There is no FW on the way, server and client are in same subnet. I getting similar logs when using websocket, and MQTT+SSL. But I did not run packet capture for these cases. IOS app is working without problem in same setup.

Android version: 10
App version: 2.5.3 (420503003)

Please let me know if you need more info.

Error message:

2025-01-28 09:48:14.019 I [DefaultDispatcher-worker-1] MessageProcessor$resendDelayWait: Waiting for 2m before retrying send
2025-01-28 09:48:14.041 I [DefaultDispatcher-worker-3] MQTTReconnectWorker: MQTT reconnect worker job started
2025-01-28 09:48:14.376 I [DefaultDispatcher-worker-3] MQTTMessageProcessorEndpoint$connectToBroker: Connecting to ssl://owntracks.example.com:8883?# timeout = 30s
2025-01-28 09:48:15.044 E [DefaultDispatcher-worker-3] MQTTMessageProcessorEndpoint$connectToBroker: MQTT client unable to connect to endpoint because the connection was lost
java.lang.IllegalArgumentException: Invalid UTF-8 char: [a]
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttWireMessage.validateUTF8String(SourceFile:111)
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttWireMessage.encodeUTF8(SourceFile:1)
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttConnect.getPayload(SourceFile:22)
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttWireMessage.getHeader(SourceFile:19)
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttOutputStream.write(SourceFile:6)
	at org.eclipse.paho.client.mqttv3.internal.CommsSender.run$org$eclipse$paho$client$mqttv3$internal$CommsSender(SourceFile:117)
	at org.eclipse.paho.client.mqttv3.internal.CommsSender.run(SourceFile:376)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:462)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:929)

[ckrey]

There is a hint in the error messages java.lang.IllegalArgumentException: Invalid UTF-8 char: [a]

Would you double check your parameters for the connection (clientId, user, password, topics, etc.) do not contain special characters?