This has been an on and off issue for my fenix 5s, but became really bad after the v.12 update, when I enter a new workout and delete an old workout in garmin connect, and then sync to my fenix 5s, both workouts (old and new) would show up on the watch, if I modify the workouts in garmin connect, that change is not synced to the watch. I have tried syncing through garmin connect app, using garmin express through my desktop for multiple times, neither works.
Did you get a solution? I have an issue with a "custom" workout that won't get sent to my 5 plus. In addition, there seems to be no way to edit the workout "type" to set it to "run" in order to see if that is the issue.