The Fiend swipe attack needs to go

I just figured they screwed up the planetary atmosphere on Aqua.

Seriously though maybe it's the lack of walls and close spaces that the game can't handle. Somehow that huge enemy's supposed to be caged, because that works flawlessly

Something like that. In close quarters he's limited, especially with additional enemies funneling one another. As such there's not a whole lot of options for him, and his teleport serves as a failsafe. As it's usually (exclusively?) the host who freezes, it has to have something to do with the peer to peer communication. If there's too much space for enemies to move in (and collide with each other when there's no hard walls funneling them) the client-host-client information processing seems too much for xbone.

Sigh, a self-respecting game company would've removed such a broken enemy ages ago, at least until they got all his problems fixed. They've been trying to field-medic him for months while he should've been hospitalized.

Since the last patch or two, I haven't seen the issue where the Fiend's model visibly glitches, does anyone know if they fixed that? About five or six weeks back (?) I saw it pretty often, Fiends physically glitching, especially during death animations. Picture below in case anyone doesn't know what I mean.

You missed a couple things.

They need to just completely remove Fiends from the MP and replace them with a slightly nerfed Behemoth(slightly lower health, or maybe can only go into rage once)

I hate playing Kett mainly due to Fiends, their glitchy as all hell, constantly teleport around, will sync insta kill you after a teleport with no warning, there swings and sync attack always seem to catch you even if you are 15 feet away and in the air. Not to be forgotten, like every other time one swipes at you your game crashes. (Which I literally just had happen a minute or 2 before posting this)

There is nothing wrong, same thing is in single player, they do teleport and they do weird swipes. IMO, it is the engine which cannot handle normally rendering of their oversized models. They are simply too big for the maps and their anchors are probably off the textures. Working as intended.