Charge 5 won't sync nor charge

[Zenpi]

Hello community.

Since this morning when I tried to sync my fitbit with my Android Pixel 4 to check for my sleep, the syncing does not work. Also I noticed that navigating the fitbit though the menu feels laggy. Now, trying to charge the watch fully I see that the batteries are stuck at 52% (with the lightning sign that indicates charging).

I already tried the following:
- Restarting the watch a couple of times
- Restarting the phone
- Restarting bluetooth
- Reinstalling the App
- Removing the fitbit from my bluetooth devices
- Charging

I just bought the fitbit a couple of weeks ago. 
Thank you very much for your help.

Moderator Edit: Clarified subject

[Zenpi · Accepted solution]

What I now did was to reset the watch like this, following. After this pairing, syncing and charging works again. All the data on the watch is of course gone, but the app registers the "new" watch and has all the data still since the last sync.

How? Go here:
https://help.fitbit.com/manuals/charge_5/Content/manuals/html/Update,%20Restart,%20and%20Erase.htm
Scroll down to "Erase Charge 5" and follow the steps. (I was not allowed to post a screenshot of that)