Assassin’s Creed Unity runs with a rather unstable frame rate, with microstutters here and there, especially during the most crowded scenes. Reddit user Strangledclown posted a thread suggesting to play offline in order to mitigate the issue.
While there’s no final evidence that the method actually works, I did try it, and it does seem to help. Other users on the thread and on NeoGAF confirmed that this seems to be the case.
It’s possible that the game might be bogged down by its online features, that seamlessly bring your friends’ avatars into your game asking for help in their co-op missions or to let you invite them on yours.
It’s also relevant to mention that frame rate won’t suddenly become spotless, as this seems only to mitigate the problem without solving it fully. If there’s any truth to this, it’s also most probable that it might work for Xbox One and PC as well.
Whether this is true or a simple placebo effect, it’s hard to say, but trying can’t hurt, even if playing online with friends is really quite fun. In the meanwhile, Ubisoft is working on an update that might help make things better. Hopefully looking for workarounds won’t be necessary anymore soon.