For some reason, when this object has a mesh collider attatched to it, the object falls through the floor upon startup. This doesn’t happen with any of the normal colliders. What could be happening?
Complexity of collision geometry can be an issue with mesh colliders. Unity’s collision detection works best when mesh colliders are convex - that is, concave meshes can have issues colliding correctly. The cylinder mesh is convex, though, so I suspect the issue is that your ground is a concave mesh collider? To confirm this, see if the cylinder collider falls through a big, flat box collider.
The floor probably has a mesh collider as well. You can’t have two mesh colliders collide in Unity. If the floor is not flat and you can not give it a box collider, you will have to give your object a box/cylinder/etc. collider.