Not sure this will help, but you mentioned ‘unpairing’ so possibly going back through the pairing process - using a domestic truck’s connector, since pairing with a German vehicle won’t work ( at least that was the case a few years ago when I paired mine) - might do it. Good luck.
I just had to recode my +AHMU module back in following a dealer software update, but before I did that, the trailer lights wouldn't even come on. Sounds like your coding is stable.