I was having the same issue. Charge 2, not syncing on an android app. I tried the tracker restart. Tried turning bluetooth on my phone off for 10 seconds and turning back on. All the troubleshooting recommendations. What ended up working was disconnecting my device from the app. When I went to reconnect it would find my tracker but not pair. In the setup help it recommended shutting down my phone, restarting my phone then trying to reconnect the tracker. This ended up working.
I wish I'd tried shutting down my phone prior to disconnecting my device from the app. I lost my data from last sync and maybe this would have solved the problem without losing the data.
I'd recommend restarting your phone then trying to sync. I'd also recommend following all the troubleshooting steps on fitbit.com prior to disconnecting the device from the app. I'm glad I got it to work though. Hope this helps.
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