Update June 22: As promised, Google Maps has updated and once again works in Android Auto. All is now right with the world.
Put this one squarely in the "that's niche" category, but it's still a thing. Android N Developer Preview 4 keeps Google Maps from working properly in Android Auto.
Some in our forums note that it's only navigation that's not working. Others of us can't get it to properly launch at all on the head unit.
And it turns out this is a known thing. From the support and release notes:
The version of Google Maps included in Developer Preview 4 (9.30) crashes when used with Android Auto. This issue will be fixed in the next update to Google Maps (9.31), expected in the coming weeks.
So there's that. If you absolutely depend on Google Maps and Android Auto to go about your day — and you're running the Android N DP4 — it might be time to roll back. And remember that it's a developer preview.