I had the same issue along with others while using my charge 2. I recently bought the Versa 2 and I haven't experienced any syncing issues. I think I was having problems because the charge 2 was almost four years old.
Best AnswerI don't think age is the case as when I called FITBIT about it, they acknowledged that since the IOS update there has been a problem. I was wondering if anyone has found a solution and/or is FITBIT still working on it or not?