I factory reset the Router and reapplied the configuration from backup but still not working. Seems like the USB is gone with the upgrade.
Edit: the hEX Routerboard is recognizing the same USB stick.
Why a USB to Serial Converter? My PC has a USB port and the Routerboard has a USB Port. So is a Serial Converter really necessary? Why not using a USB to USB cable?So only way is to use usb to serial converter and after it appears in Ports, enable Console on it.