Welcome aboard to our Community @MrsZiola. It seems the syncing problem persist across different devices as you mentioned; since is affecting your mobile device and your computer. I recommend to review PeterFitbit's post regard syncing recommendations for mobile devices.
On your computer make sure the dongle is recognized. If the dongle is not being recognized, this text will read "USB Dongle Disconnected". If you have the dongle plugged in and are still seeing this message, please try plugging the dongle into another USB port on your computer and see if it is recognized once again.
Let me know how it goes and hope this helps.
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