(sorry for the double post)
Hi,
I come with news about this "issue". I did what you said but I'm still not eligible. However, I noticed that every single castle or town that has been taken for a while by my faction (sometimes by my party alone) is given to one of the same three lords. You can see it in the picture below.
The three guys that are always eligible:
Now if you take a look at their fiefs, they already have some, so it's not like they should have the priority, according to what you said earlier (you can't see it here,but there are also 4 clans with 0 fiefs in this faction). It's like the game is stuck in a loop where a settlement is taken, given to one of those guys, taken again by the ennemy, then taken by my faction and given to one of those guys etc.