Just to add that I was playing around with this bug and found that I can rotate floors if I do it before trying ceilings. Once I apply a ceiling texture, or even just click on the ceiling box in tools, the issue returns (can't rotate floors).
I am not sure if you have already fixed this problem but I came here looking for a solution to the same thing. and I found a solution by just clicking around on things. If you have the Ceilings by Room selected you won't be able to rotate it. rather use the option next to that saying Ceilings by Tile and then you should be able to rotate it. Hope this helped ✨
