I tried this on the Helya encounter in Maw of Souls, tried Shadow Priest too, same thing. He basically will not DPS Helya or her adds. Tried with Tuanha's Druid routine and Millz Shadow Priest routine, using Enyo for 3.0.
Update; it seems this happens if the bot thinks ur not in range of Helya or her tentacles. Going close to them will make it DPS them.