The lag happens in all instances - the new ones, leveling dungeons, guildhests, everything. More times than I can count, I've found myself essentially "stuck" while the game refuses to process the ability I just used while simultaneously refusing to let me complete another one. I'll cast, for example, a Cure II, but the heal will not go off. It lets me begin casting another spell, but will continually interrupt the cast until, several seconds later, the first heal finally lands.