I understand this might be difficult to pinpoint since it could be anything, but on the Kalecgos/Brutallus tries everytime I tank I would occasionally get short freezes, fps dropping drastically to cause this effect, then it eventually clears after 2-3 short freezes. I'm thinking its addon related since it happens sometime after taunting, probably Omen doing this? It never happens on trash tanking though.
Basically the point of this post is to see if anyone else had the same issues and can pinpoint from there.
Is the raid taking a lot of AoE damage at the same time when these "short freezes of low fps" happen? i.e. lots of health bars changing at the same instant, involving a big amount of combat log events in a very short time span.