Can you replay a certain mission in AC Syndicate?
Solution 1:
If the memory is listed as 0% sync, that means you haven't finished it yet and thus you can't possibly replay it (you automatically get 50%-100% sync by completing the mission, depending on its bonus objectives). This particular mission can only be completed once you've cleared the rival gang out of the Whitechapel area, so make sure you've done that before trying to find it. Then you'll need to find the mission start on the map and go there to play the mission.