i have these red cylinders that should slide into these slots. It works great in the middle of the object with the slots. But at both ends the red cylinders keep falling through the slots and land on the surface of the object underneath. I added some pics. Maybe someone can help me out. Thank you.
I think you may have edited the object after applying the RB, delete the the current RB sim and reapply with collision type as mesh.
edit:i think I know the problem your object does not move, normally rbs are added to moving objects by default, yours doesn't, causing some problems, i tried recreating the scene and ended up with messing in the sensitivity panel and the dynamics parts, what you want to do is try adding a small amount of sensitivity, and disable the dynamics in it, reply if this worked.