I have just bought an adapter and I am going to try my own test, it could have just been the adapter he had, lets hope that is the case. I think he said he thought the issue was to do with the lanes it was using but I don't think that's how it works when interfacing via USB.
usb 3.1 controllers picks up pcie lanes iirc.
i would definitely love to know of a known to work with acorns usb to m2 adapter. as i have the feeling my current two mining mobos may wind up with some acorns on the wrong side of the PCH as the 1080tis i want to pair them up with. of course the usb may be on the wrong side too but i think it depends on which usb ports i use on the mobo.. wont know till the Soon
(tm) to be released gpu boost miner arrives.