If you open the map and zoom out fully, some statistics will appear, showing you everything that there is to do in the game (story missions, side missions, outposts etc.).
If you've completed all in that list, then you've completed the game, regardless of the percentage that the Ubisoft Club app is showing
The bug is with the app, not the game.
And I've read somewhere on these Forums that this bug should be fixed in the next Club update.