Pixhawk Mavros loss of TX but maintains RX

While flying my pixhawk in offboard mode today, something strange happened.

My setup is this: The pixhawk 2.4.8 (AC3.6) is connected to a companion computer onboard the drone, which provides the RTK GPS data. The onboard computer is connected to my laptop through wifi. At the same time, the pixhawk has a radio controller connected to it but isn’t actively used.

During the flight today, my laptop lost all pixhawk status. I switched the drone to RTL through my computer, and yet it worked. After landing the drone, the pixhawk’s log shows no lapse in GPS data, but in the companion computer log, the pixhawk IMU and MAG data stopped when my laptop lost the pixhawk status.

So it appears that the pixhawk lost the TX, but maintained the RX? The warning was “[ WARN] [1455210163.990088860]: CON: Lost connection, HEARTBEAT timed out.”
I checked the usb cable but found nothing abnormal. Did this happen to anyone before? It would be great if you can share your findings.

Thanks all!