Its the area effect of poison strike, wither, and/or whatever else they're casting. Hopefully a fix for this is in our immed future... please?
I had to rename my "pets" different names & set separate attack macros for each to send them in different directions to fight.
It kills their combine strengths and is a real PITA but a workaround none the less.
It also appears that the skeletal dragons got a unpublished debuff. I may be wrong but I always put animal lore on my necro before going for the dragons.
Seems they're not spawning with as high stats or skills as a couple months back, disappointing to say the least since hardly no one uses them anyway.