I've had this issue in a couple of ways.
In Boss Pit using Spectral Drakes White skill to possess Atrium in stage 2 caused multiple crashes for me. I reported it and was told it was a connection issue and they closed the ticket. Since then, Spectral drakes White Skill should be ready to fire, but it doesn't highlight or let me click it in boss pit. I'm not sure if they disabled it in that setting or what, but he just hangs out, full energy doing a whole lot of nothing.
I have also had the issue in which the minion he possesses does nothing once possessed. Most frequently, I notice it when Cauldron Fiend is possessed, but I've had it happen with crabs as well. This occurs often in both Challenge/Mountain and GW. Personally, I haven't experience this in Crypt, as others have mentioned.
Additionally, if Spectral Drakes white is supposed to possess the foe with the highest intelligence, I don't understand why he is possessing minions when an intelligence based hero is in the opposing line. I do not buy that a "no stat" minion has higher intelligence than a Dark Dracul, Unstable Understudy, or Cyclops Shaman, especially when I am fighting in Temples that are significantly higher level than I am.