Did you check to make sure notifications are enabled on the tracker?
Checked the settings in the Fitbit app?
Phone settings -permissions -fitbit
Phone settings -apps -fitbit -permissions
Check that the phones power management is not managing the Fitbit app?
Let's go to the help doc
How do I get notifications from my phone on my Fitbit device?Receive call, text message, calendar, and other notifications on your Fitbit watch or tracker if you have a compatible phone.
My Fitbit device isn't receiving notifications from my phoneTry these troubleshooting steps if you're not receiving notifications