I struggled with Bluetooth syncing. It would work flawlessly at times, then have periods of repeated failures. I finally just gave up on it. At the end of my ride, I sync via wifi, either at home or with my phone configured as a wifi hotspot. That always works.
I haven’t seen this mentioned elsewhere, but if I don't reset my trip data, any new rides show up as segments of the previous ride, which I hate. And if I reset my trip data before syncing, I lose my data.
It drives me nuts to be struggling with technology, while I'm out for a ride in the countryside. I want my technology to disappear.
So, for me, the Nyon is standalone until I'm done my ride. Then I sync via wifi and clear the Nyon trip data. It makes for a much less stressful ride. I've heavily customized my Nyon screens, so I see everything I care about on the Nyon.