Yesterday I was using the Google Maps app and every time I tried to change the mode of transportation away from driving it would crash giving the message "unfortunately google maps has stopped working". I tried rebooting and clearing the app cache to no avail. I then noticed in the Play store an update was available for it which I clicked on and installed. The auto update setting was checked so why didn't this happen automatically? Not even a notification was given saying there was an update available (unless I missed it). I could see this being a huge problem if apps randomly stop working and you don't know why and have to go through the Play store manually to apply updates.
It could be that the new update needed an extra permission. If that is the case, your app won't update automatically. It needs yo to accept the new permissions first.