I spent half an hour on chat with Garmin support today about this problem. Their final statement was "that's weird".
FW 3.0
If I perform either a USB/Garmin Express sync or a Wifi sync, the information on the Strava segment leaderboard gets partially erased. Specifically, the "Recent Best" and "Last" times are wiped. The KOM and "Rival" times are unaffected. I have to perform at least one Bluetooth/Garmin Connect sync with my iPhone to repopulate my times on the Leaderboard. Is this normal? I went through deleting the segments from the Garmin and reinstalling via USB sync.