After getting two less than useful stock responses from Garmin Support I reached out to Strava.
They suggested they've had several reports of segment sync not working with software v10.00 and that I try regressing to v9.20
I did this and Strava segment sync is working perfectly again.
Looks like Garmin has broken something with v10.00 :-/
Since the latest Garmin Connect update the connection to Strava is questionable. I have deleted and reloaded both mobile apps with not success. Ride is showing on Garmin Connect but will not load over to Strava. Anyone with any ideas how I fix this?