Look like a nice install.
I think he mean move to other side of windscreen, but that would just bring you over closer to the car GPS so i am not sure that would do any good.
Besides the GPS mouse antenna are now made for glass install, so its flat bottom face upwards, only the very first SG cameras had GPS antennas that was really meant for on dashboard install, so many of us had to take it apart and flip its inside to mount it on the windscreen.
I have 3 Dashcam antennas on the top left corner of my windscreen, and one in the top right corner, but my little car dont have anything as smart as build in NAV or for that matter aircon.
But as i said before all those antennas and cameras have no impact on my phone GPS.
What about if you slide the dashcam off the mount while recording, and move it as far from its mount as the wires allow, i wonder if that have any impact.
It is strange, the norm is the cameras interfere with satellite and DAB radio, messing with car GPS are new to me.
Are you sure the car GPS ( antenna ) are in the dash where you say ? could be its just the main unit thats there and the antenna are in the windscreen or near where you have the camera itself.
But as i see it there are not much outside of trying all manner of powering and wiring the system to see in any other combination resolve the issue.
You dont have to be nervous about using all the sticky pads you have for camera and antenna, i am sure Jon at SG USA can mail you more of those if you run out attempting to find a solution.
If you take off the camera GPS and try it in other locations, dont stick it in place at once, i have some times had a GPS antenna wedged in between my headlined edge and the front of the roof/windscreen for temporary installs.
Regarding the camera itself you cant really do much as it is in the best "only" place for that.
What about the wire for the rear camera, do that pass by the car GPS, i would also try with the rear camera unplugged just to see what happen then on a test drive around the block / neighborhood.