I’m having the exact same issue as @zfigz .
put in cm3+, flashed according to instructions (tried both versions). then, when pushing the button for 3s nothing happens. indeed tty.usbserial[etc] is only visible to my host when holding down the button, and the led never turns yellow and immediately off when I release the button.
I also tried to flash latest raspbian image from https://www.raspberrypi.org/downloads/raspbian/ to it, as suggested by zebra (chose “stretch lite”, should be ok right?) and got the same behaviour, button doesn’t seem to really boot the thing. should it? are we facing a HW issues?
I gave up and updated the “old” CM… forgot to try and flash the latest norns image to the old CM, will maybe do this evening… though way more fun to check out all the great new things, massive thanks to everyone involved!
edit: forgot, I’m on macOS. usbboot compiled on 10.13 with a warning (not error) I can’t exactly remember. but this shouldn’t matter if I get to recognize norns in disk mode does it?