Hey, just found a way to use Garmin Edge 820 without the start-stop button ... this will be useful for the units with broken button. So, to make it start use the autostart feature and then when you want to save ride just keep the power button pressed until device restarts , after restart completed the screen were you are asked to save ride appears . Hope will help all you guys with broken start stop button.
So, I've just had the exact same proble, with my new EdgeExplore 2. Two frustrating rides trying to get the thing to work. Glad I found your post. Really disappointing that in 7 years Garmin still havn't altered their instructions to make this aspect clear - it's so counter-intuitive.