USB:
- If this happens using USB, use a different USB cable, it's the number one culprit
WiFi:
- Make sure battery optimization is tuned off for: Android Auto and WiFi Launcher
- Check that phone Bluetooth doesn't get disconnected, that will trigger WiFi disconnection as well
- If you have the possibility try changing between 2.4Ghz and 5Ghz.
- Observe if disconnection happens in same spot, it can be caused by interference, which is more common then expected.