Hello,
I am using the folowing setup:
laptop - usb - arduino with usb shield - usb - arduino pro with ftdi
The arduino pro sends data over usb to the arduino with usb host shield, the arduino sends the same data to the laptop.
In a minimal sketch setup using sample codes from arduino everything works until… I make a move
I tested over a 100 times, if i leave everything alone it works for over 10 minutes stable.
Whenever I move my hand near one of the boards it stalls.
I am using a external power supply for the arduino with usb shield (needed to power the usb bus).
The analog ports are pulled to ground using a resistor.
I am suspecting an grounding issue but do not no how to proceed.
Thanks for reading without smiling 
i am getting mental.