Inspired by this post I manually changed the 2.4GHz radio channel to the same channel as the AP. (which normally happens automatically) And 2h15m later, downloaded around 25GB, did a lot of speedtests,.. and still works.
It never worked for so long so maybe they are on to something there.
I’ll let you know if it failed again. Otherwise I’ll come back 2 days later to say if it still works. If I don’t forget…