My rides on Apple TV 4K are not saved to Garmin and the fit files are corrupted so manually uploading to Garmin Connect does not work either. I tried it both with wifi and ethernet and also forced the Zwift app to close after the ride.
I had the same problem where rides weren’t saved on Zwift Activity history, and therefore not synch’d to Strava/GC. Reinstalled the Zwift app on ATV4K has resolved the issue.