GPX Data Doing Weird Things

Hi,
I have a Garmin Edge 800 sitting on my handlebars, and a Virb Elite on my helmet. If I want to export a video to YouTube, I generally import the GPX file produced by the Edge 800, but of late, this has been having strange effects.

Tonight, I create a video where I'm pulling up at red traffic lights. But the speedometer tells me that I'm accelerating from 8 mph, all the way up to 65 mph.

On a bicycle.

Something I'm doing wrong?