OH3: OH3 looses communication with Mosquitto

[hafniumzinc (T)]

@JoakerJa

I choosed MQTT Broker not MQTT system broker connection

OK, so you didn’t do these steps?

@JoakerJa

4. I went in the main menue to the item MQTT system broker connection
5. Connection Name: MQTTBrokerJA / Broker Host: localhost / no further settings

Or did you do these after this step?

@JoakerJa

7. I press MQTT-Broker

As @binderth says, it really would make this a lot easier if you just showed us your configuration. For your MQTT Broker Thing, please go to the Code tab and copy/paste everything there in-between code fences.