This happens in a ren'py game whenever you load a save that takes place in a scene that is now outdated/changed in some way or another. It can be literally anything that changes in said scene that causes this to occur.
I believe this is the reason why the game recommends that you save ONLY in the bedroom as it is highly unlikely that the bedroom will change in any way whatsoever.
If you didn't load a save and this just happened, well, I tried to help... Maybe try the rollback option if you didn't already? That tends to work.