I don't know if this glitch is confirmed yet.
But a friend of mine was talking about
Spoiler
A Praetorian boss battle on marine SP
And the there apparently is an elevator, if you get in the elevator no aliens will come in and hurt you they will just sit outsite of the elevator. Apparently this works for all elevators too.
I haven't tried it, it is just what I've heard. He was playing on PC.