Shame you can't send the Audi back for an exchange
But yeah there has to be some correlation. 6 devices can not be a co-incidence, so there has to be something else causing some interference.
It's clear that your not going to get a Note 4 that will circumvent this issue now, I would maybe consider just buying a standalone GPS unit for the car and save yourself all the hassle.
I'd love to use a standalone GPS, my car has one built in, but I'm heavily addicted to Waze. I like the crowdsourcing portion of it and find it irreplaceable.
I'm looking into a GPS repeater. I think the issue is that the Note 4 has a weaker GPS antenna which for most people doesn't matter, but with the metallic windshield degrades the signal just enough for it to drop out often like mine does.