I just got my Fenix 6S Pro watch yesterday. It will sync to the app sometimes, sometimes not...but it shows up as a Garmin 6S Sapphire in lieu of the Pro on some display screens in the app. Biggest issue is that it will not let me use Pacepro and says that my device is "not compatible". Same for the Spotify feature.
I have tried resetting my watch, turning my iPhone XS off, redownloading the app multiple times, and no luck. Anyone else have this issue?