Reverting back to the factory image seems to be the pre-requisite.
Well, it makes sense, but I reverted the firmware to the original 2018 one (Android 6) and no... unfortunately that is not it.
While on the ¨"Community Edition¨¨¨" ROM. I just imaged the 1GB working SD one into a 16GB fast SD and it worked in the first time it booted. Having just booted, some ¨"storage device removed" notification appeared on the Kodi GUI and in the next boot it was again at the same non booting state.
The problem doesn't seem related to the ROM.