Mauch 016 - PL-2-6s BEC Failure

hi there, absolutely love the cube and the high quality products that surround it. I have had my bird flying for a little while now. countless power ups and flys with zero issues. but just randomly the other day I went to fly and had zero power. pixhawk would power up via usb. and after some back tracking with the multimeter i found this

the sensor and the pixhawk both live in a sealable food container with a small breathing hole for the barometer. so zero chance of water ingress from moisture. it also lives inside its CF case

the mauch bec board itself shares the same solder joints as the battery connector on the PDB.

the specs of the powertrain are:
6s cnhl 5000mah LIPO
40a hobby wing esc
2nd BEC for powering servo rail

any ideas as to why this would happen? did I just get unlucky with the board? is it possible the battery did a surge upon connecting and blew the BEC?

and lastly is there any way I could stop this from happening again. as the whole point of this drone build was for ultimate reliability

thanks and all the best, pilchy