In reply to elliot.baker:
Do you have another device that you could try pairing with to check if the issue is with the phone / connect app?
Not quite the same fault but my instinct solar stopped syncing for some reason last year . With a bit of back and forth to Garmin ended up being told to do the following:
"For this issue please can you try doing a full reset on the device.
To do this please follow the steps here.
You can reset all of the device settings to the factory default values.
Hold MENU.
Select Settings > System > Reset.
Select an option:
To reset all of the device settings to the factory default values and delete all user-entered information and activity history, select Delete Data and Reset Settings.
Once done you will need to pair the device again, If you have trouble pairing the device please follow the steps below.
Remove any entries for the device in the 'Garmin Devices' menu of GCM, per "Removing and Adding a Fitness Device in the Garmin Connect App"
Remove the device from the phone's Bluetooth settings
Sign out of the Connect Mobile app
Force-close the Connect Mobile app
Toggle the phone's Bluetooth OFF
Repeat the above steps on any phone/tablet the device has been attempted to be paired with.
Toggle the device's Bluetooth OFF
Power-cycle both the phone and the device
Toggle the phone's Bluetooth back ON
Toggle the device's Bluetooth back ON
Open the Connect Mobile app
Sign back into the Connect Mobile app
Take the phone and the device outside (to avoid potential interference from other devices)
Attempt to pair the device in the Connect Mobile app once more"
Cheers,
Stuart