With respect to the 45 second rule... this applies only at startup. If the car is put in gear before the system is booted, it doesn't matter how long the car has been on or driven after that, the lines will still disappear. I have never had the backup lines disappear when I have given the system ample time to boot. I'm not one of those people that like to throw it in gear the second the car has started, so maybe those that are constantly in a rush see it more often. One of those "YMMV" I suppose.
I do wonder how much of the infotainment bugs are the fault of the Google (or Apple) vs. the infotainment system itself. Seems like with every update to
Android Auto, new bugs appear. Seems to be more cell phone and software related.