In "An Exalting Experience" in Frostfell, The Frozen Corrival stopped taking damage from my toons. I had quickly dispatched him with one toon this evening, but when I swapped to the next toon, it couldn't be damaged. I tried force exit and re-entry, swapped to a different toon, with high level mercs, but no deal. Interminable combat until I forced close. Previous nights this holiday, at least two other toons took him down per correct strat in short order. It somehow borked for me between toon swaps.