His mobility was clearly down a notch from previous and it showed. Watch the game again, he was visibly not putting almost any hard pressure on his ankle (stops, twists, turns). Very timid and slow, and not in a "basic rusty preseason game" of way, but more in a "the guy just had one of the most brutal ankle injuries imaginable" of way. He can still get by because of his vision, smarts and skills but that's not a 25 minute defender in a 100 point team.
Again, maybe he just doesn't trust that it holds yet and it's more of a mental thing that should fix itself rather quick. But that wasn't a very good performance (standard being Suter previously) and a lot will depend on where he goes from here.