Can someone explain to me how I'm flying underground in this flight?  Note the arrow on the satellite view shows the location of the arrow/data on the statistic.

This was flown at the historic Mills Mansion - ABOVE GROUND - in Springer, New Mexico.

I've been getting some pretty flaky reports from my flight logs, showning outrageous [and untrue] distances and altitudes since my controller was replaced with a GL-300-C.

Any ideas on what's going on here?  Compass was calibrated at the home point before flight.

Google Earth shows that the land there is pretty flat so we can tell that the numbers are incorrect.
But until more flight data is available to assess, A Robinson's answer is about the best you'll get.
Post a link to the PhantomHelp analysis if you want to find out more.

I'd be interested to see if there is a pattern in altitude shift during the flight from start to finish - not just at one point.

That's my point. I took off from a point that was the road at the same elevation as the point below the P3. I took this photo with my Nikon D800 just prior to flying. The position of the P3P is shown as a triangle at the time the data shown is incorrect.

For clarification: The position of the home point is the position I was standing when I took the photo attached. Note that I am below ground level seen [shown in the photo - aka, I am pointing the camera up] taking that photo. The P3P was well above the take-off point.

You didn't even notice the ghost looking out the upstairs window.

Maybe being influenced by 'something' that's 5 foot underground

Just another detail; the Phantom's altimeter is a barometer, and as such its precision is not perfect. Even the "altitude" of the Home Point can drift by quite a lot during the time of a flight.