Eclipse Paho MQTTv3 Java client loses working WebSocket connection to mosquitto 2.0.11

[42i]

Setup:

• mosquitto 2.0.11 (on Ubuntu)
• Java client Eclipse Paho MQTTv3 version 1.2.5 (maven)

Connection:

• WebSocket
• no SSL (private network for test purposes)

Symptoms:

• client can connect
• client can receive data
• after a while (a few minutes) the client disconnects
• I see these exceptions on the client side:

Exception 'java.io.IOException' occurred in thread 'webSocketReceiver' at org.eclipse.paho.client.mqttv3.internal.websocket.WebSocketFrame.<init>(WebSocketFrame.java:193)
	at org.eclipse.paho.client.mqttv3.internal.websocket.WebSocketFrame.<init>(WebSocketFrame.java:193)
	at org.eclipse.paho.client.mqttv3.internal.websocket.WebSocketReceiver.run(WebSocketReceiver.java:104)
	at java.lang.Thread.run(Thread.java:833)
Exception 'java.io.EOFException' occurred in thread 'MQTT Rec: blech' at java.io.DataInputStream.readByte(DataInputStream.java:273)
	at java.io.DataInputStream.readByte(DataInputStream.java:273)
	at org.eclipse.paho.client.mqttv3.internal.wire.MqttInputStream.readMqttWireMessage(MqttInputStream.java:92)
	at org.eclipse.paho.client.mqttv3.internal.CommsReceiver.run(CommsReceiver.java:137)
	at java.lang.Thread.run(Thread.java:833)

The very same client under the same conditions works fine with a mosquitto broker 1.6.x .

I tried to locally build a 2.0.11 / 2.0.15 mosquitto on a rocky linux I have here, but did not succeed. My system's libwebsockets is not compiled with LWS_WITH_EXTERNAL_POLL and from there it went on and on and on... Should I manage the local build and gain more insights, I'll add them here later.