This could have several reasons.
netXSPMUSB is using "libusb" to access USB devices.
The used "libusb" V1.0.22 has a problem if it finds an USB device containing an incomplete or corrupted subdevice installation.
In this case, a all further USB device scanning is stopped, resulting in not showing any USB devices at all.
If such a brocken USB device installation is fixed or the device with the brocken installation is deactivated, libusb will work correctly again.
An indication for such a problem could be the log output from the netXSPMUSB DLL.
This log is always created during start-up and can be shown by using DBGWIN (see this FAQ...).