Same problem - tired restarting (3 times in a row), removing fitbit as paired device, running down the battery, syncing to my laptop instead (didn't work).
My fitbit is a replacement from June 2017 ...... not good.
Same here, just about ready to give up and order a Garmin. It's been going on for weeks now - sometimes takes 10-12 goes to sync, battery on FitBit and phone draining all the time, everything re-set, re-installed, turned off, turned on. Am told it is a problem with software compatibility and that FitBit need to catch up with Android's latest OS version - but it's been weeks and weeks. A data freek like me needs a daily data feed! I'm constantly training for events and need to see my stats regularly, not once a week when the sync decides to work - am losing days due to capacity issues.
If a manufacturer offers a service i.e. compatibility, then they need to keep up! Sorry, I'm not being of any help to you but am sympathising!