The ac issue also stems from being knocked out, entangle, and other holding spells which drop ac. I've noticed that sometimes a full relog is required to fix your ac.
Had entangle drop my ac from 28 to 16, tried un equipping and re-equipping gear, this only seemed to lower ac due to parry bonus not applying correctly after the fact.
This is not a constant bug, but it is repeatable. Anything that seems to drop stats, ac, to hit, and so forth seems to occasionally get stuck in it's decreased state every so often, requiring a relog to fix it.