Re: why does android auto not work after marshmallow update?
Sadly, the MM update has caused LOTS OF ISSUES, with most every device, some bad, and some not so bad. Regardless, it's my opinion, that since this issue started, apparently, after the update, as indicated by the original poster above, I would recommend a Full Factory Reset of your phone, by going into "backup & reset" in your settings.
I would be sure to back up your phone to your pc, get all of your important photo's off the phone, and use app(s) like Smart Switch and/or Helium. Helium backs up all your app data, in order to keep your save data on your favorite apps. Do some research, and be comfortable with what''s being backed up.
Bob, without exception, I do a factory reset after every major update, I don't wait for issues to arise, in my opinion, its a win-win when you do it after each major update.
Hope this helps!
Chris