In Aug 2018, I bought a used 2017 500L Trekking from the original dealer with just under 20k miles. I noticed while driving around the area, the XM radio would lose the satellite frequently (no big deal, I live in mountains with big trees, so it happens) but I couldn't understand all the dead air. But on a road trip through mid-Atlantic, the Garmin GPS was doing weird stuff (I've used Garmins for 15years, even added Ireland's maps & used it there). I can't identify any specific cause - we didn't go under a bridge or large tree; there was clear sky from horizon to horizon or light rain; no bumps in the road; etc. And I can't duplicate the problems. On multi-lane, divided road with heavy traffic, we had 3 consecutive right exits/merging onto new road from left coming up in about a 2 mile distance. The GPS said something like "recalculating" but that wasn't exactly it and told me to prepare to turn left (no left turns anywhere along this road And it's an old road). The second time it happened it said something like, "Finding the route" (like it says when you first put in a destination), and the map it came up with was NOT the road where we were. A couple of times it did this twice in immediate succession, like "Finding the route", glitch "Finding the route" but the second one was our location.
I called Customer Care and they advised me to have a dealership check it out. I chose the closer dealer (not the seller); they plugged in a code reader, said no codes, couldn't duplicate the problem and so couldn't do anything until it failed. I had asked if they could re-boot, re-install the software - I'm not clear if they said they did that or they couldn't do that. (They did say everything was up to date.) But I was advised to take it to the selling dealership & maybe they could "use their money" to fix it or just wait til it fails & bring it back. I asked: so since I've complained about it prior to end of warranty, will the warranty cover it when it finally fails and their answer was no.

I have a code reader - I know it wasn't throwing codes. It's not consistent; I know it's not due to bumps in the road so probably not a wire. I'm comfortable with Garmin external devices and, sadly, will cover myself on future trips. I have a 2014 Passat with onboard NAV that I installed the updated maps with no probs.

Does anyone have any suggestions? Thanks.