I am no tech guru... Maybe Double Helix can explain what's going on.
It could just be atrocious netcode for sure.
While I'm not Double Helix, I can try. This is some serious issue with their lockstep networking.
Most if not all fighting games use a form of lockstep networking. This means the session networks your button inputs and ONLY your button inputs. Sometimes some extra data, but due to the nature of lockstep you want to be sending minimal information down the wire.
The best way to think of lockstep networking is you're playing on your console. Your console then simulates an invisible Controller 2 plugged into your console having it's button's pressed. The buttons it presses it gets from the other person over the internet. For all the simulation knows, someone is actually playing with you on the same Xbox. Your button presses are sent the same way to the other person's console.
This... they arent even playing against each other past a point... the life bars arent even synced... the match just stops for one player when the other player's game has a lifebar hit zero.
Life bar / health data is not sent over the network in lockstep usually, so not surprised to see the lifebars not update in sync. Neither person is truly host, it's up to the lockstep networking working correctly for both boxes to stay in sync with health bar information.
This is... I mean, I've watched it once, but my brain is having trouble wrapping itself around what is going on. If this is totally legit, that's not just a few errors in syncing up, that's game-breaking stuff going on.
If you can't have any faith in what is going on on the other person's screen in the exact same fight, how can you play this to any serious level?
It's legit. The simulations drifted apart, but the button presses are still being received and processed.
The craziest part is how you can see it resync at times mid match, then desync. At times you can see the characters doing the same moves in different screen positions.
Yep. It gets a couple of lucky resyncs, but drifts again. They're doing the same moves in different positions because their Xbox is receiving the button inputs and playing them on the local simulation.
I can't watch the video from work, but can't this be just an effect of the rollback? If the game is lagging badly, it's normal to see characters teleporting or repeating moves, as the netcode tries to keep the sync.
Rollback needs a proper state to work. The state went out the door and has taken a bus on a shopping trip. It'll be back in 5 hours.
It doesn't pit you against AI, not sure where you got that. But it is fucking strange and my brain can barely comprehend what's happening with the desych stuff.
It does seem to happen with the local replays too. I've atleast seen it going through survival, sometimes I get a fight that plays out differently and messes up but still seems to keep the inputs. So a combo gets missed/blocked and it puts it out of wack, as my character then does random moves from full screen that I didn't do and it diverges from there. Online replays haven't done this for me yet, but it's super weird.
And this might be a deep engine issue if LOCAL replays drift. The interesting thing about lockstep networking is if you get lockstep networking working in the first place, you pretty much have most of the groundwork to do local game films and replays. If a film can drift, this means the engine may be having determinism problems. It could be a specific move is bugged, the input playback engine is bugged, or the simulation's framerate is not properly being accounted for and a drift occurs there.
Determinism is the idea that an action will always result in the same reaction across all boxes in the session when you press a button. For an example, in Halo firefight: I press the B button to melee. Everyone else's box sees me press B, my Spartan punches on their box. My punch was in front of an Elite, which connects with the elite. The boxes all know the elite should be dealt 25 damage, and the Elite should play his rage animation. The HP of my spartan or the elite and the engine command to play the animation are not networked. Only the button press. So that effects or AI won't respond the same way every time you play the game, boxes will share a random seed at the start of the session, and they'll use this seed so the dice rolls always end up the same way for everyone.
Lockstep is great when it works but it will bite you in the ass hard if you let it desync. Async (like versus mode in FPS, MMOs) can fix itself but it also consumes tons more bandwidth and by it's nature, everyone is slightly out of sync for the entire game - something you don't want in a fighting game.
It's certainly fixable, but there's definitely a bug in the engine here, and doubly so if drifting occurs in local replays.
They're littered throughout the video. I'm not saying it's an AI opponent but there is AI taking reign and you're fighting it when the desync happens, paired with the delayed inputs coming through. The game has to be taking control at some point, it's not a cut-dry case of the inputs just being delayed.
No AI is taking over. The button inputs from the other player are being processed, but since the simulations have drifted apart, the same button inputs won't always produce the same output on both boxes.
If AI takeover was a thing, it would have noticed DSP's box shut off the networking when he went to the victory screen because the match was over (hence why the other player just freezes - they're not longer being fed inputs, so the networking is properly waiting for new inputs to arrive), assume DSP left, and replace him with an AI.