I had a real issue with connecting my Jaybird X3's to my Vivoactive 3 Music, after a bit of google acrobatics trying to find a fix I saw that while many (most) seem to have issues with this headphones and garmin watches in general, some reviews and people seem to have no issues at all.
I tried resetting my headphones, tried turning off any bluetooth device within 10 meters etc. the problem was always the same. I could pair the headphones no problem but no matter what they wouldn't connect.
So I finally reset my watch, not the data just settings and re-paired, after that I've had no issues at all connecting, no drops.
While not a questions, as I had so much problems getting this to work and Garmin support never lists try reseting device I wanted to leave this here for prosperity.
As I found one post here from like 2 years ago asking about the exact same issue but with no responses and it got me thinking about "Wisdom of the Ancients"