My new Sony Xperia X Compact(Android7.0) can get pairing with Garmin Edge 520(12.10) but can not get communication with the Garmin Edge 520 through garmin connect apk. To make trouble shooting, I installed nrF connect for mobile and nrF toolbox for BLE apk from google play.
The nrf connect scanning and logging got continuous "gatt error 133" that means common BLE connection error, then running nrF toolbox, finaly to get establish to stable connect the Edge520 until power off.
It suggest that garmin connect could have bugs or handle connection establishment by software improvement.
I hope gamin developers deal with this issue in the future and sorry for my poor English.