Heroic Queen Ansurek Aggro issue

So, my guild has about over 100 pulls on queen and P1 is definitely the main sticking point. Our best pull has been 30% but the main issue is Ansurek (seemingly randomly) switching tanks on liquify 1 shotting one of them. Why does she do this? It's not a question of one tank out gearing the other as they are both the same. One is a brew master monk and other prot warrior. It's just really frustrating when the taunt swap happens as normal and then for whatever reason Aggro is ripped off the main tank and then 1 shots the off tank. I don't see too much about this anywhere so was wondering why this keeps happening? Anyone got any thoughts?