Try to reset both, Oregon and GSC 10, then retry the procedure
Can't pair Oregon 450 with Garmin GSC 10 cadence sensor (they compatible by Garmin).
To pair the GSC 10:
Navigate to Main menu
Select Bike Cadence Sensor
Press reset button on GSC 10 (white button)
Wait for Reset button to flash red/green
Select Search for New
Pedal bike to see alternating red/green blinks on GSC 10 reset button
Bike Cadence Sensor will show Connected when pairing is successful. The touchscreen GPS will pick up cadence through the GSC 10. Speed will come from the satellites.
NOTE: The Oregon 200, Dakota 10, and Rino 610 are not able to pair up to a GSC 10.
Is the solution Downgrading Firmware of Oregon 450 (now using version 6.60)?
Any help, please