For some reason, despite the fact that I've assigned background speed in room properties, the backgrounds do not move. However, when I deactivate all the instances, the backgrounds begin to move. Also, rooms which use converted compatibility background layers from 1.4 seem to be moving just fine. I have no idea what the cause could be, it seems to be some internal glitch. All of them were working just fine a few days ago, but all of a sudden (without me modifying the project) they just stopped working.