Pixhack : can only initialise if safetyswitch pressed


I just flashed a new Pixhack 2.8.4 board with the last plane firmware.
When the firmware is sucessfully flashed, I have in the console :
[MAV 001:1] Initialising APM
[MAV 001:1] Check BRD_TYPE: px4io start failed

I have found that I needed to press the safetyswitch during boot, to flash the IO firmware.
When doing it I hear the sound of the sucessfull io firmware flash, and then the board boot correcly.
In APM Planner I can see the move of the board in the “primary flight display”, and everything seems to work nicely.
But if I stop pressing the safety switch, the board seems to freeze, and I lost the link.
If I restart the board, I’am a the first step : “px4io start failed”

What can I try ?

Thank you for you help