Mein Gott, this is such a mystery. On my test machine, #Signet works fine on #Qubes 4.2, with a USB qube, even when the USB qube is disposable.

I'm trying to figure out WTF is going on here. Aside from slight differences in hardware, there's not much different between the test machine and my desktop.

#FDE is up next to test. That absolutely shouldn't make any difference, but it IS a difference in the config of these two systems.

If that works fine, then I guess it'll be time to try restoring some qubes from my backups to see if that is somehow making a difference (again, it absolutely should NOT be able to even cause this level of problem, but there are just so few differences at this point, I'm throwing out all my assumptions until I get to the bottom of this)