EZUHF and Pixhawk inteference

I wonder if anyone could help here…
Running Arduplane 3.3 and latest firmware (1.52) on EZUHF with 8 channels via Ch1 PPM Muxed.
TwinDream plane with 2 Castle Creation 50Amp ESC’s - 1 feeding the Pixhawk (max 5A). Have tried a variety of different positions for the EZUHF but continually find the Pixhawk going into RTL (pre-programmed) from the EZUHF failsafe. I have swopped out both the Pixhawk and EZUHF with spare ones 3 times with the same result. Immersion RC 700mW VideoTx and HiTec micro digital servos.
The video link below shows the extent of the problem:
A near disastrous flight Bin file can be found at:
dropbox.com/s/5nh7fwgnuy1dn … 5.bin?dl=0
Any ideas appreciated!