@Cat2B it's near impossible to theorize when you've provided us zero specifics about your environment; tracker firmware version, which app and or platform (iOs, Android, Windows) you're using, manual or automatic sync, what's proceeded these problems, etc. Try turning off Bluetooth. Let Fitbit turn it on. This fixes more than half of syncing issues.
Thank you @Williger. Killing the Fitbit app, switching off phone Bluetooth, starting up Fitbit app and letting it start BT fixed the issue for me in a Moto G8.
Don't know if this is a phone BT issue or Blaze issue.