My instant and immediate knee jerk thought, since it is an intermittent problem is to look real hard at your ammunition. If for some reason your not getting a good solid resize on the base, it's gonna stick.
Coffinmaker
PS: And just for funzies, I'd pull it completely apart, thoroughly clean and de-grease everything that moves (or not), the apply fresh grease and oil. Then take a real hard look at your ammunition ...... again.