Some Android Auto users seem to be facing a baffling issue with the platform. They claim that Android Auto disconnects whenever the vehicle passes over a speed bump, even if it was just a light bump and regardless of the cable being used. Some thought that there were issues with their cables or the car's ports, but even with changing cables or cleaning, the problem persists. And they notice that the phone is still charging and the OEM mobile interface works.
Some were able to fix the issue with a firmware update, but it's still hit or miss. Google is aware of the problem and is asking those affected to supply more information to determine what's wrong.
Source: Auto Evolution