Object falls through terrain

I have a game object created in Blender and imported into Unity.
The object has a rigedbody component attached and collider (mesh)
However the object falls through the terrain whenever its in the scene.

Ive tried raising the object high just to make sure it wasnt sticking through the terrain and I can’t turn off the gravity as I need that to be active.

Any ideas how I can stop this happening?

Changing the objects mesh to ‘Convex’ seems to have fixed the issue.

Thanks to all those that answered, trying out your suggestions helped me solve it