Adding an Extension Cable or Hub to a Previously Recognized USB-to-Serial-Port Adapter causes serial device to be reconfigured.
NetBotz and RS232 sensor connections using USB
If you add an extension cable or hub between the appliance and a
USB-to-Serial-Port adapter or hub after the USB-to-Serial-Port adapter
or hub has been connected to your appliance, all of the serial ports on
the converter are recognized as new ports by the appliance.
previously configured serial devices on these ports, use the Serial
Devices task to reconfigure these devices.