On PlayStation 4, we ran into problems where sudden frame latency spikes would occur for extended periods, causing gameplay to stutter in a stop-start fashion - the issue here is that we are seeing 60-100ms pauses manifest during the action, easily noticeable when playing, and noted on our frame-time graphs (however, frame-rate is an average, so this stutter is smoothed out to a certain degree). Regardless, the end result is an obviously poor gameplay experience.
On Xbox One, we encountered a different issue entirely: a sustained drop in performance so bad that it could only be due to something going seriously wrong with the game's rendering code. The problem started after dying, with other players unable to revive our avatar - the reviving animation would kick in, but after it had finished we would just fall down and die again. After finally getting brought back to life a minute or so later we were confronted with truly horrendous sub-10fps frame-rates for an extended period, resulting in a stuttering mess of slide-show proportions. At this point, the game was unplayable, but we continued on to the next mission objective, and after a few minutes the problem subsided; the stuttering became less pronounced, but it didn't completely go away until we quit the session and returned to the main world.