Same for me -- Android Auto ran perfectly UNTIL the MM update was applied (via T-Mobile) on my LG-G4. Now the Google Maps app freezes and Honda factory head unit becomes non-responsive. Only solution is to unplug phone. And, strangely enough, sometimes even though the screen is frozen the voice directions remain on and working, while the map display is several miles / turns "in arrears."
OK, thanks to everyone that commented / offered solutions to my LG G4 problem. Here is a recap of what I have done from "mixing and matching" these comments to get to a temporary fix, along with a recap of my configuration.
Recap: 2016 Honda Accord with OEM head unit. LG G4 T-Mobile phone with recent OTA update to Marshmallow. No problems using all functions of Android Auto prior to MM update. After MM update, experienced frequent screen freezing, yet with occasional continuation of voice directions and music while display screen was otherwise frozen showing the maps and clock at an earlier time. Also occasional display "blinking" and even flat refusal to recognize the G4 when USB cable inserted.
What seems to at least temporarily fix this while otherwise keeping MM update:
On phone:
Go to settings>general>developer options (see another post how to enable developer options in MM)>select USB configuration
At this point, select MTP (media transfer protocol). You may have to do this more than once for the phone to "take" it -- you can check this by going to some other screen, then coming back to this to be sure it has been selected and remembered.
Then settings>general>smart cleaning
At this point, delete temporary files & raw files (caches)
Then clear all running programs by touching the square symbol at the bottom of the home page and selecting "clear all."
Restart phone
Plug into USB cable in car. If asked whether to allow USB communications, select "yes."
Now it should work again. Hopefully Google will soon offer an update to either AA or MM to fix this so we all don't have to go though these gymnastics.
Again, thanks to everyone!