As far as I know you need to fix the problem in a program like Blender. There you can change the amount of polygons of the collision mesh, or something like that. I personally have no experience with this, so hopefully someone else can share more information.
If the problem is only at one location, you can maybe add an extra entity with static rigidbody and primitive collision component as a workaround.
Probably a bad triangle. Ammo has issues with some triangles of its trimesh. This is often happens when the same mesh has triangles of very different scales. Just open Blender and try to “redesign” that triangle, e.g. cut it in two, or swap the diagonal of a quad from left-to-right to right-to-left, etc.