is your module in MBIM mode?
Just did a test in Ubuntu PC, no problem is found for my EM9291 module:
owner@ubuntu:~/QMI/MBPL/MBPL_SDK_R44_ENG5-fwdwl.bin/SampleApps/fw-download-tool$ sudo ./bin/fw-download-toolhostx86_64 -l fwdwl.log -f /home/owner/Desktop/EM92_FW/02.17.08.00/ -m 4 -d /dev/ttyUSB0 -p /dev/cdc-wdm0 -t 1 -w SWIX65C_02.17.08.00.cwe -n SWIX65C_02.17.08.00_GENERIC_030.081_001.nvu
[sudo] password for owner:
Application version: 1.0.2412.2
INFO: QDL Port: /dev/ttyUSB0
INFO: Device Path: /dev/cdc-wdm0
INFO: Device Port: 0-0
INFO: FW Path: /home/owner/Desktop/EM92_FW/02.17.08.00/
Target image Info:
Carrier :GENERIC
FW Version :02.17.08.00
Model ID :SWIX65C
Package ID :001
PRI Version:030.081
SKU :9999999
Switching device into download mode for image switch ...
Modem Needs FW
Modem Needs PRI
Waiting for modem to disconnect from the host ...
Modem disconnected from host.
Waiting for modem to come up in BOOT and HOLD mode ...
BOOT and HOLD Mode. Downloading firmware ...
Downloading: /home/owner/Desktop/EM92_FW/02.17.08.00//SWIX65C_02.17.08.00.cwe
Downloading: /home/owner/Desktop/EM92_FW/02.17.08.00//SWIX65C_02.17.08.00_GENERIC_030.081_001.nvu
All image data was downloaded successfully.
Device is about to reset ...
Waiting for modem to come up in ONLINE mode ...
Modem is now in ONLINE mode ...
FW update status: Successful
FW info from modem:
Model ID : EM9291
FW Version : SWIX65C_02.17.08.00
Carrier Name : GENERIC
Carrier PRI Revision: 030.081_001
Firmware download process completed successfully.