I had it happen again sunday. this time i was in a dungeon. i had been playing most of the day on and off with no issues. I decided to go into Zul'farrak for some transmog stuff and i had all the bosses killed except for the last boss, i noticed that there were still corpses on the ground. turns out slot 3 and 4 stopped attacking/looting sometime before the hydra boss. seems completely random, maybe something to do with loot a rang. cause i dont remember this issue until i started using the loot a rang to loot.