It can't be related to Daimyo's losing control of vassals, since in my game where it happened, I haven't even appointed any Daimyo's. That means I also can't transfer these new vassals back to one of my other vassals, since I don't have any Daimyo to place them under.
It would indeed be nice if someone could tell us how this is happening.
EDIT: Thinking about it, if one of my Kokujin would conquer a province and he already has 5 Kori, then he would release any new Kori he conquers to me, not having a Daimyo title of his own and thus not being able to have vassals. It still don't know how it happens when you're only having Daimyo's as vassals though. In my current game I had three vassals, all Daimyo's, when suddenly I ended up with a couple of extra Kokujin and one of the Daimyo being down to 2 Kori, instead of the 5 he had.
It would indeed be nice if someone could tell us how this is happening.
EDIT: Thinking about it, if one of my Kokujin would conquer a province and he already has 5 Kori, then he would release any new Kori he conquers to me, not having a Daimyo title of his own and thus not being able to have vassals. It still don't know how it happens when you're only having Daimyo's as vassals though. In my current game I had three vassals, all Daimyo's, when suddenly I ended up with a couple of extra Kokujin and one of the Daimyo being down to 2 Kori, instead of the 5 he had.
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