I have TrainingPeaks set to sync workouts to Zwift.
The sync works. However rather than syncing the day’s workout once, it syncs the workouts once for every time you start a Zwift activity that day (as opposed to the correct behaviour of just syncing them once). i.e. it doesn’t recognise that its already synced them, its just re-syncs them as a second copy. Launch a third activity in Zwift and you get a third copy, etc etc etc…
(ignore masking of workout titles/structure and other data)
