Ubisoft Entertainment recently returned to Assassin's Creed Black Flag Resynced and released a small update 1.0.5. It is designed specifically for the PC version of the game; it has not been released on other platforms.
The exclusive update is purely technical - it does not add new content, but is designed to solve a common problem with "stuttering".
The developers of Assassin's Creed Black Flag Resynced addressed the players:
Ahoy, pirates! We've released a PC-only patch (1.0.5) to address stuttering issues some PC players have been experiencing. We've already received confirmation that some players have had the issue fixed by this update, however, if it persists after installing the latest version of the game - please let us know via the Bug Reporter tool.
Overall, players praise Assassin's Creed Black Flag Resynced. The AC IV remake received "mostly positive" reviews on PC via Steam. After 21 thousand reviews, the game's rating was 77%. The developers did not specify when they plan to release the next "general" update for all platforms.