Problem with launching the game (Assassin's Creed 4: Black Flag)

Help solve the problem. The game, purchased from Uplay, does not start. When you try to start, it shows "Synchronizing your achievements" as expected, but after nothing happens, there are no errors.
I bought it on Steam, and there are no problems with the launch. The most interesting thing is that if you go to "Offline" mode in Uplay, then it starts.