I have cycling activities that get merged via SyncMyWorkout, but with the last two Garmin software updates (latest 24.12), the deleted data has come back. So months of activity are being added that were deleted.
Also, the activities that I’m merging are not being kept as Garmin Coach activities. Even activities on my Cycling computer have been changed to non-Garmin Coach activities, even though I started them as a Garmin Coach workout. Usually, this happens when I’ve started it on my watch as well (for HR data) and accidentally saved the watch and computer data.