Domoticz

The webinterface shows general info about e.g. errors.
Before I reported about unhandled MQTT messages. I was adviced to check with mqtt explorer.
I was unable to trace the errors. Now I wonder if there are more error-logfiles somewhere in the OS.
-Bart

If it's easier for you (as for me), you can enable logging to a file, modifying /etc/init.d/domoticz* (if you're using Linux) and restarting domoticz.

To debug messages exchanged by MQTT, you can also subscribe to all topics by using the cmd (from linux shell)
mosquitto_sub -u USERNAME -P PASSWORD -t '#'

Also check the troubleshooting wiki how to activate Domoticz logging to a file https://wiki.domoticz.com/Troubleshooting