EM7455 does not reach BOOT and HOLD mode

I want to upgrade the old firmware.
Have 3 EM7455 here: 2 of them from Fujitsu Lifebook, one from unknown source.

Under Linux Ubuntu
compiled successfully fwdwl-litehostx86_64
did most steps from lite-fw-download-readme.txt
ModemManager deactivated, blacklist Gobi drivers (no effect recognized), sometimes cdc_mbim module / driver loaded (no effect recognized), started from “cold”, deactivated network etc.
tried about 50 times in the last ten hours

invoked (in proper dir)
sudo bin/fwdwl-litehostx86_64 --fw path ~/Downloads/SierraWireless7455_JulianE559/FWfolder/

result “other modem”: “Firmware download process completed successfully.”
Works fine. Does not help: Modem does not function in this Laptop anyway (BIOS whitelist??).
Means:
Setup is fine, can work, did work with one of three EM7455 modems.

Problem:
both EM7455 from Fujitsu (one was updated successful some years ago) show:

Waiting for modem to come up in BOOT and HOLD mode …
Modem not coming up in BOOT and HOLD mode in 60 seconds. Please check parameters. Application terminates.

So both do not enter the BOOT and HOLD mode.

Question:
How can “not enter the BOOT and HOLD mode.” be resolved?


log says: (please pardon line numbers and privacy edit)

211 Application version: 1.0.2307.1
212 INFO: QDL Port:
213 INFO: Device Path: /dev/cdc-wdm0
214 INFO: FW Path: /home/###/Downloads/SierraWireless7455_###/FWfolder/
215 Target image Info:
216 Carrier :GENERIC
217 FW Version :02.38.00.00
218 Model ID :SWI9X30C
219 Package ID :000
220 PRI Version:002.082
221 SKU :9999999
222 Switching device into download mode …
223 Modem Needs FW
224 Modem Needs PRI
225 Waiting for modem to disconnect from the host …
226 Modem disconnected from host.
227 Waiting for modem to come up in BOOT and HOLD mode …
228 Modem not coming up in BOOT and HOLD mode in 60 seconds. Please check parameters. Application terminates.

Does it work in windows exe upgrade?

no, it does not.
I tried the 072/02.33 and the 082/02.38 versions as exe file, root. Starts properly, fails. Quite sparse message, try to take a note and report here if I manage to do so.

If you type at!boothold, does DM port come out?