Objects with physics crumble into one place.

I beg for every Unreal Engine user’s forgiveness for existing.

All the objects you see flying have Simulate Physics turned on which wasn’t an issue for a while, but now for some reason every object with physics just crumbles into one place, and
also the AIs stopped working, they refuse to move.
The NavMesh just disappears as soon as I hit Simulate.
If someone has encountered the same issue before.
Please help. I’m a complete beginner.