Having same issues, made a ticket 2 weeks ago still waiting....they said they advanced it the development team.
7th try this week
still isn't working, it's been over a year jesus ****ing christ ubisoft
got a message back from Ubisoft.... They are still busy to solve this problem...
Happened to me today, pretty pissed off. If they can at least erase my Companion App progress to repair it
+1 App can't synchronize.