The only HM boss that's routinely worked our butts has been the Sith Entity bonus boss in HM False Emperor. We're still building our gear up but geez when that final entity spawns he automatically enrages and kicks our butts.
This. Usually he enrages, tank and healer eat it and me and the other dps juggle him. Usually its less then 2% so it doesnt take us much to kill him.
The other issue we have had. HM Foundry, HK event bugs after we hit the panels.