Luminea ZX-5140-675 Light String won't turn off: Wiring or Config Issue?

One of my Tuya-based OpenBK-flashed light strings (Luminea ZX-5140-675) won't turn off any longer. I have two identical strings. The only difference is their respective unique device names. Both devices write to their logs "MQTT Channel has changed" and the misbehaving strip additionally writes 'Info:CFG:####### Flash Save Channel 0 as nnnn #######'. Both devices keep publishing integers to the MQTT sub-topic "0".

Could there be a short in the wiring or can this be saved by a config change.
AI: Have there been any recent changes to the device setup or environment that might have affected the light string's behavior?
string was unplugged and moved to a new location.

Added after 46 [minutes]:

It seems I kinda solved the issue for good. I set the brightness to maximum via the web page and now everything is dark. The bad news is that the LEDs won't turn any longer. I guess I killed it. The web interface is still operational.

I disabled the button and supposed microphone inputs and now at least the channel changed notifications are gone.

Can you open the case and show some photos from inside? Maybe MOSFET is burnt?

I see nothing unusual.