Right now it seems that only GPS is used for navigation when driving with Android Auto. Normally this is not a problem but when driving into tunnels, the marker on the map doesn't move anymore because the GPS signal is lost. As soon as you leave the tunnel navigation resumes normally, but this is a problem when, for example: you need to take a ramp/roundabout exit/change highways in the tunnel or right at the exit before regaining GPS signal.
Could it be possible to navigate with "Dead reckoning" if AA provides speed via its API? This could also allow to guide on complex intersections underground, because right now that is not possible without GPS signal.