Last night, I encountered an invincible Cerberus Assault Trooper in Mass Effect 3's multiplayer. No matter how many times he was shot, his health would remain full. I don't know if he was finally killed or if he just disappeared (because I wasn't looking in his direction when this happened), but eventually the game moved on and told us the wave had been completed.
And that's not the only error I've encountered in ME3's multiplayer. There is of course the well-publicized gravitational pull of the Banshee (I have no idea why that hasn't been fixed in an update), but I've also encountered three other oddities:
1. This is rare, but there are times when lag (I'm assuming) will cause enemies to seemingly jump around on the screen, making it difficult to get a fix on their position and avoid their attacks. It's as if time is being stopped for the player in short increments.
2. One time, my character started falling through empty space as if I had stumbled upon a bottomless pit. And I seem to remember that there was another spacial error leading up to it. (My character was positioned high off the ground if I remember correctly.) Never happened before or since. Very strange.
3. A few times, I've noticed that one of the other players appears to be hovering around the stage with both arms on one side of their body. And except for floating around the stage, their body appears to be completely motionless.
What bizarre glitches have you all encountered in Mass Effect 3 or other games?