I got a new Fitbit Sense. I switched it on, it synced with my app and then started a firmware update which was going to take a while so I went off and got on with my day. When I got back I had done an additional 2500 or so steps once the Sense firmware finished updating I pressed Sync on the app and it didn't see my Charge 4, connecting the Sense had kicked it off. I re-connected the Charge 4 and it was reset to the earlier step count throwing out the 2500 steps I had added. Hardly a major problem but iritating none the less.
The moral of this tale is, only setup your new Sense when you have plenty of time to wait for the firmware to update.
You cannot have Sense and Charge 4 on same account. If you went through Add a Device, even before getting to firmware update, it should have noted you already have a Charge 4 and asked if you wanted to remove Charge 4 so you could use your Sense.
It depends if you are connected via WiFi or Bluetooth. Once i made a mistake to update my wife's Sense via Bluetooth and it took literally hours.
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