Character falling through floor

My I use a mesh collider on the ground entity, using the same ground model as the mesh. My character keeps falling through it for some reason.

It is actually a slightly different problem to one I posted earlier. Now there is not even a flat plane to collide with. It is not longer a heightmap generated terrain. Now I’m just using an fbx for a landscape, my character just completely falls through it.

If it is a different problem please don’t mention it in the other topic.