Have you checked all the areas on the map? To look for uncompleted missions? I know you had 100% but just in case the uncompleted missions are new upcoming ones.
I doubt this is the case but who knows LOL as i still have 100% it may be a glitch or something as i haven't seen people on reddit complaining about this.
Edit: Check my post https://forums.ubi.com/showthread.ph...ech-Audio-Clue