Metal Roof Questions

They used gasketed fasteners/screws for metal roofs. I'd check the rubber to make sure it isn't dried out. If it is, I'd go ahead and replace all the screws. The rubber keeps water from getting into the screw hole. If it's a small gap, it might just be thermal expansion/contraction mixed with some wood shrinkage, but the screws shouldn't just back out of the wood for no reason.
Either A. The rubber has fallen off and left a gap between the metal and the screw head, or B. The wood underneath is rotten/split to where the screw won't hold. If it's A, just do what is stated above. If B, I would go in the attic and inspect the underside of the roof. If the screw is loose and can't get a bite into the wood and there is no damage, try a longer or thicker screw. But whatever you do, make sure it's gasketed.

It becomes a problem when the roof has been installed for a period of time and that once neat little round screw hole ....is now an oblong screw hole.

Neoprene doesn't "fall off" the washer .....Odds are, the installer reached into his bag with mixed washers and installed one without neoprene.