Terrain Mesh Collider working in Unity 2018 and not in Unity 2020

I imported a .fbx file into my Unity 2020 project w$$anonymous$$ch has a terrain. I added a mesh collider to the terrain and for some reason my player collider does not detect the mesh collider and keeps falling through the terrain. Not only that but I can't even see the mesh collider being applied to the terrain when I add it, or see the mesh when I click on the terrain.

Furthermore if I follow the exact same steps and import and use the same player prefab in Unity 2018, everyt$$anonymous$$ng works fine. The player does not fall through.

Anybody familiar with t$$anonymous$$s situation and knows a fix?

Thanks in advance.