we suggest you set back to the original wall height first, so that the ceiling will connected with the walls, then set the new height of the walls altogether but not seperately on the specific wall, and the ceiling will not float again.
What worked for me was to manually set all walls to original ceiling height, one by one since I edited them lower in the beginning and that was what caused my problem. I put them back to 280cm as the wall had them before. Then went as indicated back to View > Top ceiling > Wall Height = 250cm. Then the the ceiling and walls automatically set themselves to 250cm connecting correctly. Thank you!
