I also record my TR rides on my Edge 1030+ so I can capture some data unique to Garmin Connect. When I stop my workout in my 1030 when it stops in the TR app, I don’t hit Save Ride on my 1030 until I see TR has synced to Strava. As long as I follow this sequence, I never get duplicates in Strava.
It’s also because of this process, that I noticed sometimes the TR - Strava sync is slow. But, really it’s not the end of the world as I do about 15-20 minutes of stretching/massage gun after I ride, by which the sync has occurred ever when it’s slow.