Way to flash custom cwe for the FX30 Cat-M with windows?

Hello,
We have a custom (and working) R15 firmware that we can use and update (with the fwupdate command).
When we receive FX30 from Sierra for previous release version, we usually use a .exe that flash the firmware (by calling fdt or fdt2).
Unfortunately, it seem that this is not working anymore, in general failing with this error (FX30 was connected and ping was also good on USB):

FDT version: 1.0.1702.1
Awaiting suitable port or adapter ...
Enabling selective suspend ...
Firmware download failed.
Primary error code: 82 - Failed in checking modem mode.
Secondary error code: 68 - Received incorrect response.
Device error code: 0x0 - Unknown device error code.

Is there an official procedure to create a windows installer to flash the firmware?

This is needed on our side to allow our client to use our developments.

Best regards,
Guillaume

have you installed the latest USB driver?
Also your fdt version is old, you can try the latest version here:
https://source.sierrawireless.com/resources/airprime/software/fdt/#sthash.WibNoNsE.dpbs

I also tried with latest available cdt and I use the latest USB drivers (GenericDriverSetup-V8.14.5087.0005).
Here is the same output with a newer version of fdt2:

FDT version: 2.0.2012.0
Awaiting suitable port or adapter ...
Firmware download failed.
Primary error code: 12 - No download port available.
Secondary error code: 68 - Received incorrect response.
Device error code: 0x0 - Unknown device error code.

In this example, I called fdt2 directly in the terminal:

fdt2.exe -f CustomFw.cwe

do you see the DM port enumerated in device manager?
how about you type AT!BOOTHOLD first

Yes DM port is in the device manager.
After calling BOOTHOLD and trying again I obtain the same result.
However, my device manager UI seem to automatically refreshed each ~5s when FX30 is connected in USB

Seems your usb port is not quite stable, can you try with other USB port?
can you try with another Windows PC?