This issue is caused by improper installation and uninstallation of USB drivers.
After a remote-viewer client is closed while a USB device is connected to a client machine, it becomes impossible to use the USB device on the client machine.
A new package, usbclerk, temporary installs usb drivers on a per-session basis. When the session is concluded, usbclerk uninstalls the usb drivers.
USB drivers no longer remain installed on client machines after remote-viewer clients are closed, and client machines regain access to their USB drives at the conclusion of a remote-viewer session.