Is it correct just before its disabled? As far as I remember, the code will not update any mesh colliders after they have been created, and nothing happens OnEnable - and Awake should just get called once on these sprites. I'm at a loss as to what to suggest - except to set a breakpoint / spam some debug.logs to try and find out whats going on with them.
The mesh collider mesh isn't shared and shouldn't get updated, so if something happens to it it must just be in that script, and there are very few places that could happen.