FPS slows to litterally about one tenth of a frame in combat frequently

I am not sure what triggers this but as my game progresses into the later stages I am more and more frequently getting into combat where I litterally slow down to one tenth of a frame per second. Every animation takes forever. Its unplayable when this happens. It just happens at random when entering tactical combat.

My only alternative is to auto resolve the combat, in which the very bottom unit in the summary list takes all the damage. If I auto played it it would take 15 minutes to watch. Also during this slow down, my champions forget they have spells. THis may be part of the problem. This needs to be fixed soon. It has happened sporatically to me the entire beta, and in a major war against Resoln with my custom faction, it is basically unplayable. It is not just tied to these factions but whatever is causing it could be more common with resoln and their new units?