For those still having issues, download the latest version of Pulseway for Slackware. As of Pulseway 6.1, they added support for newer libssl, which seems to have fixed issues. May have to update your symlinks, as well.
Sorry to dredge up an old post. I just added pci-stubs to my config, and it didn't change anything. Rebooting the VM (or shutting it down and starting it from the GUI) makes all the USB devices on the card I passedthrough disappear. Very strange, but probably just a quirk of my hardware.
Just double checking--is this still the case? Every time I reboot my Windows VM (e.g., to install windows updates), my USB devices no longer show up and I have to reboot the whole server.