UPDATE FROM STRAVA:
Thanks to everyone who replied to this post. Garmin has notified us that they have an firmware update that should resolve this issue. If you are still experiencing this, please ensure your Garmin device is updated. If you continue to experience problems after that, please reach out to Garmin Support directly for further assistance:
Hi
I have two Garmin devices which I sync regularly with Strava. My Garmin Forerunner watch syncs perfectly every time. However, in the last few weeks my Garmin Oregon 700 only partially syncs. I only get the first part of the activity (typically 10-40%) appearing on Strava. The whole activity appears fine in Garmin Connect, so I assume this a Strava problem. Please could you advise.