Mesh Colliders seem inaccurate in producing a proper collision mesh around an object. In some cases a corner of a wall can be the death of a player as at the right position a person can push their player through the mesh. If words are to describe the collider its that it seems thin and doesn’t take well to corners or edges. Are there any ways to adjust a Mesh Collider using additional scripting or adjust the players Character Controller so that a positive response between the two colliders are met.
Consider increasing the vertex density of your meshes, and use a fairly consistent density of vertices in all your physically interactive models. I’ve found this can add to the simulation’s stability. Where possible, use simple shapes for collision meshes and tailor their complexity to meet the requirements of your game mechanics, while being as simple as possible. Avoid concave meshes wherever possible.