I just noticed mine had become set to another device for some reason. It has never done this in ten years of using it, was always set to the device on which I had the app, no matter if I changed my device which I did several times. Inexplicably today I noticed it was set to the last device (tablet) that I had the app on. Had put it onto the tablet temporarily as I didn’t have space on my phone, but i could only deal with no notifications of phone calls or messages for so long. So after a few months I found space and set it up again on my phone. I deleted it entirely from my tablet, and had unpaired my Fitbit from Bluetooth.
FIX
I deleted the mobile track “device” from my account. Then went to “add new device” and set it up again as I did originally when I was a new Fitbit user all those years ago, when it worked fine until now. Hopefully this works for you too.
