I have not been able to get a USB Dongle that runs fine under Vixen 3, to work with Xlights when running with a Falcon 16v3.
The warning message comes up "Another Process....is outputting" and x Lights literally freezes. I have to force quit. My system is Lubuntu 18.04. If I deactivate the USB and just have E1.31 running, things are ok..
I had to move my DMX network over to a serial output off of the Falcon.