Problems with altitude during rides.

I'm getting some crazy altitude number and wild swings recorded during rides.

Sometimes it's almost normal, then in the middle of a ride it goes to over 100000 ft, then back to normal.

Sometimes it's all over the place right from the start.

I've got the lastest update. I've tried auto-calibration. Even that bounces around like crazy.

It used to work just fine last year. Any ideas? Things to try?

Here's a pic of my last ride. At no point during my ride did I actually reach low earth orbit.