Assassin's Creed Unity has it's fair share of bugs and glitches, and the latest update on Ubisoft's live blog of fixes insttructs players on how to get around game crashes until there's a proper patch.
Ubisoft says it's the games social features which are causing game crashes on all platforms once player hit the continue button on the main menu, and the developer commented,“The team is working hard on a fix for those players that have been affected by this".
Players who haven’t experienced the issue are advised to take the following steps to prevent a crash: don't add any in-game Recent Player entries as a game contact; if you already have game contacts, you'll need to remove them.
In order to do that, follow these steps:
My Brotherhood > My Contacts > Game Contacts (using RB/R1) > Focus on a Contact (LS) > More Actions (Y/Triangle) > Remove from contacts.
If the above solution doesn't work, you'll need to sumbit a support ticket. The issue is being reported on PC, PS4, and Xbox One.