Mesh colliders suddenly stopped working

I've been using mesh colliders on a lot of the objects in my game, and they've been working fine up until about five minutes ago. I tabbed out of Unity to work on a model, and when I tabbed back in, none of my mesh colliders worked anymore. I went into the inspector and found out that they no longer had anything selected under "Mesh", so I manually added the meshes and found that my player still completely ignored them. Even deleting and reimporting the models didn't change anything. Does anyone know why this might be happening or how to fix it? I'm using Unity 2019.3.9f if that helps.,I've been using mesh colliders on various objects in my game, and they've been working perfectly fine up until about five minutes ago. I tabbed out of Unity to work on a model (not related to the floors), and when I tabbed back in, suddenly none of my mesh colliders work anymore. I checked in the inspector and found that they no longer have anything listed under "Mesh", so I manually applied the mesh, and my player still falls straight through the floor as if it wasn't there. Does anyone have any idea why this is happening or how to fix it? I'm using Unity 2019.3.9f1 if that helps.