I recently purchased the Garmin Fit App to view my Garmin Connect activities, and (fingers crossed) to upload my FR610 data to my iPhone someday. Anyway, the first time I logged in to the app it downloaded a few of my past activities from GC, but would never upload an activity I created within the app. I noticed a few others here and reviewers of the app on iTunes had the same problem. I tried troubleshooting it many different ways with no success. However, the most recent attempt seemed to do the trick. I signed out of the app and then changed my password on the GC website. When I logged in to the app with the new password the last 100 activities showed up. Also, the activities created using the app then uploaded to the GC site.
I hope it works for others that may be having the same problem. If so, it appears there may be a login bug on the GC server.