Buggy.
I took the AA to finish her waves for commando mastery, and the arc pistol for pistol mastery. Went in with low level consumables so as not to be too OP.
(Well, also because I'm poor.)
Anyway, found myself on glacier vs collectors with two inexperienced pugs and a somewhat decent batarian vanguard, who was the host. There was some lag, but not enough to blame all the oddities on that. One of the pugs was invisible to me, but I could see their tag floating somewhere below the map. When they died (say, every 30 seconds), at first I could revive them, but later on, the activation 'button' seemed... disabled. I've never seen that particular bug before.
At the end of wave 6, a praetorian got stuck together with a couple scions at the staircase between LZ and basement. I warped one of the scions - and they all died, the whole bunch, like from a missile. I thought it was a missile, but the kill feed said it was my warp. The host quit then. I suspect he thought I was cheating, and I can't really blame him. Other than that one event though, powers and everything seemed normal.
After host migration, the invisible pug became visible, and someone new and relatively competent joined. There was still some lag, but nothing outstanding. However, I noticed that I got the 5 headshots medal again (already had 20 prior to wave 6 and host migration), then 10 headshots, again, and then later once again.
This resulted in a hilarious credits screen:

But now that I think about it, I had "hyper" stasis with the same kit in a platinum game with friends earlier today. As in, sometimes it was normal, but sometimes it would just instakill collector troopers and captains. Not phantoms, though, sadly. And I believe I was hosting that one. No mods active. Anyone around here had similar experiences?