I have more information, but no real answers yet.
- If I boot into Tails, I also have problems with Signet (I did not do as detailed of debugging to confirm that it’s exactly the same thing, but it acted the same when using the release version of the Signet client). This seems to point to a problem with the USB controller, but I’m already tried two USB controllers on the motherboard and…
- Installing a PCI → USB adapter, attaching to it sys-usb, and passing it through to a target qube has the exact same problem! I can see the client send the message, but then it just hangs.
So this one really has me stumped. I did change motherboards when I switched to Qubes 4.2, but since other USB devices seem to work fine, and I chose my motherboard based on the Qubes HCL having multiple reports that the ASRock B450M Pro4 was going to be solid.
My next steps are to test this machine using the PCI card in Tails and try to find another machine where I can install Qubes 4.2. If Signet works fine on another machine with Qubes 4.2, then I know this is a “me problem” and I can figure out if it’s something weird with the motherboard, or maybe a reinstall would fix it, or maybe I’ll figure out something else I can try.
Unfortunately I don’t have the money to just buy another computer consisting of the same components in order to test this. If I still had a high paying tech job, I’d certainly consider that option though! 
