Today I completed a workout from my training plan, but when it was time to record the workout it lasted around 15 minutes and it was not uploaded, neither to zwift nor to Strava, however I went to check and the activity was completed in the training plan.
Is there a way to upload it again?
To Zwift no, depending on your platform you may be able to upload the .fit file to Strava but chances are is corrupted.
Sometimes they can be fixed bit not in all cases.
In my training plan, the activity is completed but it doesn’t even appear in the companion…
What platform are you using?
Assuming you mean Windows you should be able to manually upload the .fit file to Strava so at least you’ll be able to get your performance data.