I am having a similar problem but with the Runna app. Workouts were not syncing across and when I tried to remove and reconnect it's not working. Mainly it seems because I cannot disconnect the app from Garmin.
Strange, I know I have tried to disconnect from Garmin under Account settings then under Account information but still it doesn't help. The connection is re-made after I try but it never syncs. In the past I had this happen. For that fix I had to be in runkeeper then when you see the privacy state you had to click on it once, then I could allow the sync and it worked but now that doesn't help. Maybe that privacy link trick will work for you and Runna or maybe it's Garmin's way of say stop using other services, we can do it all. Right now I am just exporting the data then importing the activity manually. I just have some many years of data in Runkeeper that I want it all to be in one spot.
