I had the same problems with sync and notifications. If you have an incompatiple Android phone like I do (Samsung Galaxy A5) and have tried all those help articles, you can try an application called Sync Fix for Fitbit and Huawei / Honor phones which for me settled 99.99% of all my problems. There is a 10-day trial period to validate if the app works for your phone and after you only hace to pay a single amount for life (around 6$). You have to follow the instructions and install the PERMANENT solution for it to work properly. In my case, it's been working without problems for 6 days.
