Snapping door stops                            

Maybe it will help to switch the U-brackets (eg, between right and left doors).

1. Pry up the locking collar with a par of pointed pliers.
2. Remove the metal plate.
3. Pull the U-hoop down with a par of pliers. If it is not possible to move, then use a pinch point crowbar turned upside down.
4. Clean and put grease on the U-hoop.
5. Hold it firmly with a par of wide pliers and knock it up again with a hammer (hit the pliers).
6. Put on the metal plate
7. Put on the release sleeve.
8. Put grease in the slot where the bar moves.

Or get new improved U-hoops from CXBASIS.