I presume that you have checked the Control Panel/Device Manager page for device errors?
And run sfc /scannow in a Command window As Administrator to check the integrity of the Windows files?
Always worth a look at the Event Viewer too especially for the times when relevant actions have been carried out. System log mostly, but worth checking Application log too.
Some info on a known BT issue here but I can't see fitbit getting into that hole?
https://www.techradar.com/news/bluet...s-might-be-why