[NiLuJe]

Well, if you can't read the serial output because of transmission issues, you can't really tell what's happening ;o).

In any case, IIRC, the actual force downgrade procedure on devices where the OTA updater rejects downgrades, but not the initrd updater, is to *NEVER* unplug the USB side of things. Just let it sit to hope the file has been flushed to storage properly, and then hard-reboot.

That's (probably) ridiculously easier if you have serial access, because you can sync && reboot manually. But then you can just flash it manually from diags in the first place.

But that's not even exactly what's happening here, since that's not the OTA updater, that's the initrd's recovery menu.

(i.e., you shouldn't have to jump through any hoops here).