the issue with the platform disappearing and the weird ■■■■ with the tiles is probably the same issue and looks like some kind of zsort problem. i would guess it has something to do with your material.
my understanding of post process volumes is that they need to cover everything they affect so i would scale that to cover the whole level and the camera.
i haven’t done any work with 2d stuff in unreal but unreal is cm based and you’re using powers of 2. i don’t know how you’re creating your tiles but i strongly suggest using a modeling program to create a plane and then unwrapping it for your texture layout. that will make tile placement a lot easier and less error prone. ue3 did have a power of 2 grid.
i really don’t have a clue with the lighting but i suggest you do use a light (or multiple) as that will give you more control. in your situation dynamic directional lights would probably be the easiest and they shouldn’t cause any performance issues.
the collision i don’t have any ideas on but i would guess it has something to do with your movement controller and possibly collision volumes.