No, that’s not something I’ve ever experienced.
To be clear, what you are saying is that when you start an activity with a structured workout the watch goes into activity mode as usual, you can see the workout screen and get the alerts of the steps in the workout, the workout ends without issue, you can stop the activity and you can see the activity summary etc. and see the activity in the log on the watch just like you’d expect but the activity doesn’t sync back to the app?
Do your workouts use names or have step names that use non-english characters? A total guess but I just wonder whether the activity data might be failing to export from the watch due to some sort of workout-related metadata issue.