A fun one is after a ride, go to the Strava activity page, click the little wrench and choose "create route." I'll do a ride and the Garmin will report say 1,200ft. I'll go to Create Route and it will be ~1,500ft. I'll look at the upload from my wife's Garmin 500, and it will be 1,470ft.

I had one single ride where the 520 over-reported elevation. I got caught in a downpour, the quarter-turn mount filled with water, and my elevation suddenly rocketed up 1,000ft.