Unfortunately, it seems that the latest firmware update has caused this issue, along with sudden loss of battery power, for many of us.
The best advice is to contact Fitbit support. They will walk you through the same troubleshooting procedures. If they confirm that your device is still under warranty and the procedures did not fix the issue, they should send you an email with an offer to replace the device or a discount on a different device. If your device is out of warranty, I believe they send you an email with a discount on a replacement.
Rieko | N California USA MBG PE