As Airget said, it's regen.
Tell your WHM to not start off by giving you regen, it should only be casted after the tank already established some aggro.

Also, as they guy above me said, they threw in some extra trash to block in some places as well as made some of the trash act like keys to unlocking the doors.

They've also increased speed(?) on some trash to make them able to hit the tank while he's running. Either that or they made the attack range longer for some of the trash.