[MrForbes]

If you could post a picture of the chain system, it might help us think of things to do.

Older design garage door openers use a chain and cable loop, that has a spring tensioner in it. If you think that might help you, I can take some pictures of one. But it sounds like you don't have a fixed length loop, you just have too much friction causing the chain to jump over the sprocket.

Powder coating changes the dimensions of everything...