If that’s not the case, and that’s a mesh collider then most likely that’s a known Ammo.js issue. Long triangles like terrain meshes have can cause that behavior with a capsule collider.
Possible workarounds:
- Use a sphere collider.
- Use Ammo3, I can verify this problem has been solved in that version though there is no official release right now. You will have to find the PR and build Ammo.js with Bullet3.