Syncing has always been a bit hit and miss
The Mrs and me both had a Charge 2 and syncing could be a real pain at times, taking multiple attempts before it worked. Had to send the wife's back for an exchange. She is 80 and can barely climb stairs but the FitBit thought she was hill runner doing daily marathons and mountain climbs. We've both given up on the devices now. It was interesting / fun for a while until the novelty wore off. The technology doesn't seem that reliable.