Also have at least 50k mi on Frogs and generally have no problems except when installing new cleats, I occasionally have to fiddle with the
amount of elastomer under the wedge. Once done they usually function well until the cleat wears out. I have had your problem on one set of
pedals but it has been so infrequent that I have not investigated. You might swap the cleats on the shoes and see if the problem swaps as
well, and you might try adding a smidgen of thin rubber under the offending cleat wedge if the bolts are not loose. Once I was unable to unclip
on a Frog when a cleat retention screw loosened up and jammed the cleat in place. I have also found screw tension affects the elastomer springiness
also. The blue goop on the screws is good for the initial install and should be supplemented with more threadlocker if you adjust the screw.
Here with the very small screws using blue locker is ok, small screws are unlikely to be frozen by the "permanent" blue threadlocker.