Thank you very much for your help, Hans,

I am very glad about it.

Yes, I found that wall now.

And I figured out, that this wall
takes effect on the display of the boxes: moving or removing it or adapting its height to 296 cm let the boxes display correctly. Also deleting the "room" of the big room (without changing the wall mentioned before) corrects the display. Very strange...

Many thanks for changing and sending my file, nice greetings, Dirk