Hmm, I believe those steps worked for me last time I played with that.
Maybe worth checking that the device is indeed visible in /dev/bus/usb in the container and that the permissions and ownership looks correct.
Hey @stgraber@tomp i did a fresh debian installation and installed lxc/lxd from source and tried to add a device as described above even after restarting and rebooting the machine i could not get the usb device appear in the container
root@devout:~# adb devices
List of devices attached
root@devout:~# lsusb
....
Bus 002 Device 003: ID 0483:374b STMicroelectronics ST-LINK/V2.1
...
root@devout:~# ls /dev/bus/usb/002/003
/dev/bus/usb/002/003
root@devout:~# adb devices
List of devices attached
root@devout:~# exit
logout
on the host i did add the device and the appear
aok@debian:~$ lxc config show devout
.....
devices:
STM32F4:
mode: "0666"
productid: 374b
type: usb
vendorid: "0483"
androidPhone:
mode: "0666"
productid: "6860"
type: usb
vendorid: "04e8"