@Libbiexox I think you're posting about several issues, going to try and break it down:
I don't understand how a platform can change but you don't actually have a platform in the house? Do you have a screenshot?
Could the shadow be a piece of wall of ceiling on a higher floor?
The objects being deleted, does this happen with MOO enabled? Or disabled? Does it happen when you close the room, paint the wall or place flooring? There is a bug report here for something similar
https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-Stuff-deleted-when-painting-walls-half-walls/td-p/8673542@zoiee2020's question is really helpful. There is currently an issue with the game thinking that a platform is still on the lot even after it has been bulldozed. This causes objects and building tools to not work properly. Exiting to the map screen sometimes helps, as does bulldozing the whole lot then quitting and reloading the game.