Last week I was running on a treadmill using my Airpods Pro, which were connected to my Fenix 5x Plus on my left wrist, and mid session it stopped playing music. To this day I'm not able to listen to music through the watch.
I've tried pairing the devices together again through the following route:
Settings > Sensors & Accessories > Add New > Headphones
The Fenix 5X Plus is able to find the Airpods, but when the message "connecting to Airpods" appears, after a few seconds it says: "Failed to Connect".
The Airpods work fine when pairing to my phone.
I've tried this method while the phone's bluetooth is off.