I just tested another scenario. UAL935 was NOT in MyFlights, and was in Network with no route information.
It then transitioned into my airspace, and appeared in MyFlights with no route.
I turned OFF Network, and still no route in MyFlight.
I turned OFF Hardware Flights.
I then turned Hardware Flights back ON, and route information appeared (EGLL - KLAX).
So, definately a bug, probably caused by network aircraft not having route information, and that then causes the aircraft to have no route information when it transitions into your local airspace.