Being the active driver is not the same as being logged into the vehicle/MiX ELD. If you select sleeper, off duty or on duty not driving as a duty status you will automatically be removed as the active driver. You are however still logged into the MiX ELD device and therefore the vehicle.
If you want to transfer to another vehicle you must make sure you are logged out of the currently logged in MiX ELD /vehicle using your red driver plug.
If you do not log off on the current vehicle and move to another vehicle, the new vehicle will not allow you to log in. If the vehicle that you previously left yourself logged into is accessible to you, please remove yourself from that vehicle first. If not, please see your site admin.