EM9291 in Linux Preventing Shutdown

you can see the command parameter for fwdownload tool here:

If there is no /dev/ttyUSB enumerated, you cannot download the firmware

I used this MBPL_DRIVERS_R31_ENG2-usb-src.tar.gz in ubuntu 18 with EM9291.
MBPL_DRIVERS_R31_ENG2-usb-src.tar.gz (24.9 KB)

Kernel log shows wwan0 network interface, /dev/ttyUSB0 (AT port) and /dev/ttyUSB1 (DM port) for USB serial port