In plain English, Android Auto shut down every time the driver entered a tunnel or went through an area with spotty cellular reception. The issue happened every time the mobile device lost the cellular signal.
The original poster claimed that relaunching Android Auto was a challenge, too. The mobile device believed the app was still running, so the only solution was to toggle Bluetooth and Wi-Fi off and back on to relaunch Android Auto. When the network signal was restored, such as when exiting a tunnel, Android Auto crashed again.
Many other users have reported the same behavior since June, but the bug became more widespread in the last few weeks for a mysterious reason. Everybody says Android Auto wireless shuts down in the middle of the driver whenever the cellular signal is lost, and the only way to experience a stable connection is to either drive on routes with no signal drops or to switch the mobile device to airplane mode.
Neither is a convenient solution, but no other fix seems to exist. Users encountering the glitch tried the generic workarounds, including downgrading Android Auto, but they couldn't find a fix that brought things back to normal.
An Android Auto team member chimed in during the summer and asked for additional information, but the current status of the investigation is unknown. It's also unclear why the problem has become more widespread after the most recent Android Auto updates.
Meanwhile, the only workaround I can think of is to use Android Auto with a cable. Most cars offering wireless support can also run Android Auto via a wired connection, so plug in the mobile device for a stable experience.
The issue doesn't seem limited to a specific phone brand, though, based on user reports, it looks like Xiaomi is more widely affected than other companies. However, Samsung and even Google's Pixel exhibit the same problem, so the glitch seems to reside in Android Auto rather than the software powering the mobile device.
Everybody seems confused about this mysterious problem, and Google itself has remained tight-lipped on the investigation, presumably as it has made little progress since it asked for additional feedback. However, the bug becoming more widespread is concerning, and the search giant should accelerate the bug-hunting process, especially as Android Auto crashing in the middle of the drive can become a safety issue for those running navigation on the infotainment screen.