Yes, using all the latest, but the Intel PCHC CMP PCH-H/LP Firmware v14.0.0.7002 because....1002 gives some other error.

Yes, previously it worked perfectly, but I recall getting the same error when I tried to ... overwrite the firmware with the one prebuilt by ASUS, same version, with allowsv argument.

OK, I think I found the issue, but no idea what went wrong, where or how.
When I ran the "FWUpdLcl64 -save upd.bin" command I got the following errors :
Error 357: Restore Point Image was requested, but it is not allowed because CSE is in Recovery Mode.
Error 329: Restore Point Image Failure. Reboot may be required.

Thanks again! I've never seen that "Error" message before- that's what I meant! But as I wrote: It'd be a 'nice to have', obviously this will not show up so often anyway.

Regarding 'cleaning' with a corrupt MFS partition as base for configuration- I'm aware of that, possibly the whole dump contains errors. It was just curiousity if there was a version incompatibility in addition.

Here we go.

Even weirder is that I had the same error with the 4.0.45 firmware downloaded from ASUS, using the same FWUpdate version.

Yeah, weird stuff, it worked just fine previously. New BIOS today, maybe that sorts out something.

What about the new MEI version 2041.15.0.1893 on Station Driver?
Including new MEI driver with the strange number 2036.100.0.1024

I installed the drivers from that package, INF variant. They appear newer, by date, than the previous ones I had.