Rigidbodies leap up like fleas then ignore collisions!

I have a giblet prefab that takes the place of the character who gets annihilated. His body parts hit the floor when they land - stop as expected - then come to life by leaping into the air, then hit the collider again but this time drop through after a second.

It almost looks like I scripted this to happen as its comical in nature but what makes it more annoying is the fact that it was working fine until I replaced my placeholder models with better versions.

For example - My lower leg is a lower leg model with a box collider and rigidbody. My level is a 2d curvy landscape with lots of undulations and stuff, mesh collider.

I heard that mesh collider can sometimes be a bit funny so I tested it on a new cube object with a box collider and it does the same thing...

No physic materials on anything by the way.