After many years of diving I find that my face must change on every other dive. My general go to mask, a Cressi will be perfect one day and leak like a sieve the next...
Same problem here, only add fogging to that! Some dives, no leaks and no fog. The very next dive, I may have leaks, fogging or both. It drives me crazy!
Many times, the fogging goes with the leaking because the more you breath into your mask to clear it, the more chance you have of fogging it up. But it's not always the case.