There are many comments here saying that Android Auto is not buggy - in my four years of experience, it certainly has had major and minor issues. Here is a non-exhaustive list of issues and oddness:
1. When you plug it in, it fiddles with bluetooth settings, because although the screen is sent via the cable, the audio and similar is sent via bluetooth. This sometimes results in odd behaviour and requires unplugging/replugging.
2. For a long time, when I plugged it in already navigating, the phone would show an "Android Auto has stopped working" dialogue and the car screen would go blank. I eventually found it was a conflict between Android Auto and the mini-map overlay feature of Google Maps.
3. Currently, whenever I try to use the voice assistant, it says approximately "Sorry, there has been a problem. Please try again later." Trying again later doesn't work. So now I have to pull over to change or add destinations.
4. When you choose to navigate somewhere from another app, it navigates to a place that's like 10m-100m away from it in some direction, which is sometimes an entirely different road. If I unplug the phone, set the destination, then plug it in again, then it navigates correctly.
5. It doesn't support sending messages via anything other than SMS, which is a pain when you're wanting to tell someone on WhatsApp or Messenger that you're five minutes away.
6. I made the mistake of playing a podcast through Google Podcasts (which is built in to Android Auto). Now, it just always plays it when I get to my car. I can't make it forget the podcast, and it plays from the start if it finished. I can only replace it with another podcast for it to keep playing unprompted.
7. Occasionally, it will switch destination to one from an older navigation session. Best hope you notice before you drive too far the wrong way.
8. This might have been fixed, recently, but whenever I would restart my phone, it would have as many Google Maps sessions as I'd had journeys since the last restart; however Android Auto was taking over Google Maps was leaving zombie activities/processes.
9. There have been a good few more, besides.
I still prefer it over what car manufacturers might provide, though.