I believe there's a known issue with Dismay X - Wave 3, where the endurance talismans are on the 2 MCRs... if you don't kill the MCRs first and kill the center demon spawn (which is supposed to kill the other two) it will freeze up. Is this consistent with where you're getting the error?
FWIW, I'm not seeing any drop increase by Farming X over VII, or even VI for that matter. Might be better off staying out of X and enjoying the faster clearing on a lower level.