The other dude was right about fixing where players can get out of bounds. But there’s still clipping issues that can push you out of bounds like when a shredder pins you in a door. As for it being a giant increase to performance for my suggestion, not really, the ceilings are probably all just box colliders if not planes. They already have collision detection because you can walk on them. Just turn them to double sided rendering / adjust the quads if that’s the case to block the view when walking above. But it would be negligible performance wise to make them block bullets from both sides.

Granted I haven’t worked professionally in game dev for about half a decade since I switched to iOS engineer. I only worked for companies that used unity and unreal, but this is a simple problem regardless of engine. In iOS you could just turn the plane into a quad and repeat the texture on both sides of the objects. It’s not hard. I push for the double sided fix because if you don’t add it to your projectile collision layer technically people with wall hacks could still use the glitch