The problem seems solved. It wasn't a real bug, just there were 4 unfriendly lines into the XML that caused the mess.
Essentially the SP had underlying neutrals, so for game where those were skipped 5+ players, the game engine wasn't able to split territories among the players due the low number of regions in the starting drop.
Just to be everyone on the same page, the file attached to this post is the working one, so both mapmakers know that is the file to use in future if necessary.
I'll keep an eye on games in the next hours but things should work properly now.
I'm going to unlock the map right now.
Have fun and sorry for the inconvenience that has occured.