I tried to use convex meshes with sizes around 10cm (0.1 unit) in our project, and noticed that Convex meshes do not work with my triggers objects as they should. The problem appears only with Convex MeshColliders. They start sending OnTriggerEnter and OnTriggerExit even when the object is completely inside another object. The triggers is not the only problem. OverlapBox method does not see this colliders too.

So I’ve created the examle of this strange behaviour with 100% reproduction in 2019.3 and 2020beta.

the white cubes - Convex mesh with a size 1 unit scaled to 0.1 (and the left scaled to 0.025) + rigidBody kinematic.

the blue cubes - BoxColliders scaled to 0.1 with OnTriggerEnter/OnTriggerExit methods

the red cubes - BoxColliders scaled to 0.1 with Physics.OverlapCube() method.

the blue dot appears when OnTriggerEnter is called for the top blue cubes, or when OverlapBox returnes a collider for the bottom red cubes.

the red dot appears when OnTriggerExit is called for the top blue cubes, or when OverlapBox does not find any collider for the bottom red cubes.

The bug DOES NOT REPRODUCE if MeshCollider Convex setting is off. It works as it should with non Convex Meshes.

The bug reproduces with Convex+Box. NonConvex+Box works good