Ubisoft made the announcement on the Assassin’s Creed: Unity live update page that it was social issues that was making the game crash. On the page, Ubisoft states: “The team is working hard on a fix for those players that have been affected by this.” Further, this bug affects the game across all platforms.
If players have not had any problems when on the main menu then Ubisoft recommends players not to add any recent in-game players as a game contact. However, if players already have game contacts, then Ubisoft recommends deleting these game contacts. To remove game contacts, users have to go to My Brotherhood > My Contacts > Game Contacts (using RB/R1) > Focus on a Contact (LS) > More Actions (Y/Triangle) > Remove from contacts.
Assassin’s Creed: Unity was released earlier this month on PlayStation 4, Xbox One and PC, and faced criticism from critics due to the game being released before it was ready (as seen in the technical problems). However, Ubisoft has promised to work with more quality assurance personals so this issue will not occur again.
It is good that Ubisoft is finding the source of this problem. Although, I do feel like this should have been tested more before it was released. I do hope this was a one-off from Ubisoft and that they will not release a broken game like this again.