There is another (later) thread with a huge number of people reporting similar issues here:
…people mostly report concave print beds. Replacement beds seem to be warped too. Mine is convex. So mine might counteract errors to warpage somewhat. Another reason for me to give up on trying to explain the problem to the friendly but not very helpful support people.
Bambu Lab seem to be focusing on people that want to print multicolored spongebob figurines or gingerbread houses. I came to the conclusion that I have to use other means of production when I need bigger and/or precise parts. Its a shame but you can also only expect so much from a mostly injection molded printer at that price point. 