In order to sync your missing activity to your Stryd account, you can download the activity file from your Garmin account and manually upload it to Stryd PowerCenter.

Please see this article for instructions to upload the missing activity from Garmin Connect to your Stryd account: https://help.stryd.com/.../6879378-manually-uploading...

Based on our initial investigation into this issue, we believe the most likely cause of the issue is that activity data is not being synced to Stryd by the source platform.

We expect that this issue will be resolved soon and that your future activities will automatically be synced to your Stryd account. If a future activity is not automatically synced, you can follow the manual instructions above.