First this is not a complaint just my observation. I know what happened and why it happened, I just didn't think an old H3 could produce enough RFI to cause this kind of interference.

I mounted a GoPro H3 on top of my P3A just to get another perspective while flying.  Nothing fancy just a stick on GP mount and a base model H3 with no accessories and open face frame for a fixed view turned on and off manually while grounded.

I started the P3 and controller and waited until I was given the green to fly. The controller showed good GPS signal with a bird count in the high teens. I turned on the H3 and hit record, looked at the controller and had completely lost the GPS signal. I turned everything off, repeated the start up and got the same symptoms again. I went ahead and flew around at a couple of meters just to get the test shot I wanted. After I landed I de

That's been fairly common knowledge for quite some time now that some GoPro's interfere with GPS signals.

Wrapping the camera in some foil is one known solution.

Aloha cook,

     It also does not help that you mounted the old H3 right on top of the GPS antennae.  The antennae is attached to the middle of the top half of the shell.

Aloha and Drone On!

You simply blocked the GPS signal!  The antenna is in the center of the "roof".