My Approach X40 golf scorecard not syncing with the Garmin Connect App. It syncs when I plug it into computer.

Make sure that the Garmin Connect mobile app is on the most current version (2.14) through the App Store/Google Play Store, and update if showing available on the app page. 

Check the settings directly on the watch to ensure "Activity Tracking" is enabled. The only metrics that will appear from the X40 in the Connect mobile app are Steps, Heart Rate, and non-golf activities recorded on the watch. If you are wanting to check scorecards or golf related features, make sure to check through the Garmin Golf app for that info synced from the watch. 

If none of the above apply or resolve the concern, then remove the watch pairing from your phone, and then re-pair through the Garmin Connect mobile app to see if that then resolves the sync concerns.

Contact Garmin Support if the concern continues so they can discuss and troubleshoot live with you through an expert.