If device is not seen after upgrading fw, one solution would be to look the id/vendor string with lsusb and/or use latest udev 01-cgminer.rules.
I checked the ID/Vendor, they were still the same (297 0001) if memory serves right. I'm on Windows btw.
Maybe it needed a reboot, but it detected the M1 in device manager like before, so I figured it should work. It worked before on old 0.2 firmware with W7 and 3.11/3.12.3.
I thought it was weird, so might be some mistake on my end.