Sphere collider with continuous dynamic and mesh collider issue.

Hello I am working on a 2.5d side scroll game. One of my character is armadillo and he rolls around the surface. If he uses his ability then he moves with a fast but constant speed. It was fine when I was using unity4 but after switching to unity5(5.0.2), I am having some collision issue. And this is important for my poor armadillo since this cute character reads surface normal to compute tangent direction to roll in every frame.

Okay, so the problem is as in the simplified picture I drew. When armadillo is using ability from first terrain to a neighbor terrain which are nicely aligned, collision function I got a wrong contact normal. Because of this, it changes armadillo's velocity(to stop or upward direction) after fixedupdate and before trigger functions even though I don't change it anywhere.

I don't know how to fix it and also I've been seeing some people saying avoid using non-convex mesh colliders but my project is so far ahead and can't avoid having non-convex mesh colldiers.

I need your help. Any comments will be helpful for me. Thanks in advance and have a good one you all!