The Old Sentinel glitches out after you destroy the 2nd set of regeneration crystals. The first time this happened everyone just quit out of the game. The second time it happened a giant douche bag by the name of Iceman101388 refused to kill himself and just stood there shooting the glitch IMMUNE Sentinel… and the server doesn’t timeout for another HOUR! It was explain to him by myself and another that we would at get a partial reward for the fail mission. I’ll simply quit playing this map until it’s confirmed fixed to prevent having to deal with further asinine behavior from idiot griefers like Iceman101388, which I recommend that you just search for and block him right now to save yourself any frustration.
This is on PC too. Very annoying!