Experienced 3 times already. once by myself, twice group memeber experineced one weird bug- when group approaches to boss, one member sometimes cant see the boss, and other group members sees that memeber standing in one place. It looks like when group going past fires after 1st boss, one of memeber been ported to othe version of dungeon or something like that/
Also i want to mention, 3rd boss very often is buged - one or two minions are buged and people cant hit or tab target them.
Engine guardian - best set ever