It seems to come in cycles. It is either they won't come out, or they fall out. Ever try to KO the 2 inch KO and have the 3 inch volunteer to come out first? Arrrrrggghh! Then, of course, you don't have a 3 x 2 reducing washer set in the truck. Almost enough to make you order all your cans with smooth ends and punch them all. But, I digress....
Troffers are a problem. You could contact the manufacturer for a supply of extra "sliders" for this inevitable occurance. They gotta be really inexpensive.