This is ancient bug, at least for me, both under 4.1 and 4.2.
Namely, when I attach storage device as USB to a qube, it gets lost from the qui-device widget list.
systemctl --user restart qubes-widget@qui-devices.service
won’t bring it back (“Failed to connect to bus: No medium found”)
or
$ systemctl --user restart qubes-widget@qui-devices.service
won’t bring it back (restarts service but to no avail), neither terminating qui-device from GUI task manager works.
It gets back either upon restarting correspondent sys-usb, or upon Qubes restart (which logically implies restarting sys-usb actually).
This is completely annoying for several years, so if anyone knows the solution for dummies, please let me know. If not, can someone place the issue on Github, since I don’t have an account there. Thanks.
Can you post the service log in dom0?
journalctl --user -u qubes-widget@qui-devices.service
I have corrected OP, so now the log as expected shows
Aug 18 08:32:50 dom0 systemd[2386]: Stopping qubes-widget@qui-devices.service - Qubes Widget service…
Aug 18 08:32:50 dom0 systemd[2386]: Stopped qubes-widget@qui-devices.service - Qubes Widget service.
Aug 18 08:32:50 dom0 systemd[2386]: qubes-widget@qui-devices.service: Consumed 2.107s CPU time.
Aug 18 08:32:50 dom0 systemd[2386]: Started qubes-widget@qui-devices.service - Qubes Widget service.
but widget doesn’t reappear the device, anyway.
Can you check the journalctl log in dom0 at the time when you attached the device and it disappeared from the list?
Maybe there are some related messages.
Or restart Qubes OS, run this command in dom0:
journalctl -f -n0
And try to attach the USB device to the qube so it’ll disappear and post the resulting log.