I've been with the Fenix line and Garmin since 2012 and this is the first I've ever seen of this issue.
I've currently got the Fenix 5x, which I've had no problem with regarding connectivity. Standard drop outs, but you get used to that.
Then I switched phones. I was using a Galaxy S8 initially and decided to switch back to my original Google pixel. I set the device up, paired/synced it, then went about my business. When I opened up the app a few hours later, the device had disappeared from the paired devices menu (in app). So, I went through setup again, same thing, and then a third time, same.
At this point I switched back to my S8 because no BT syncing is a deal breaker. Yesterday I decided to get the new Google Pixel 2. Went through the same steps as I always have to set up my watch.... And..... Same issue, just disappears.
Has anyone had this issue ? Is it Android 8 ? Help !!