CK II - Can't form Slavic Union by Decision

[MesserJoe]

One line summary of your issue
Can't form Slavic Union by Decision

Game Version
3.3.3

What expansions do you have installed?
Jade Dragon, Monks & Mystics, The Reapers Due, Conclave, Horse Lords, Way of Life, Charlemagne, Rajas of India, Sons of Abraham, The Old Gods, The Republic, Legacy of Rome, Sword of Islam, Holy Fury

Do you have mods enabled?
No

Please explain your issue is in as much detail as possible.
Can't form it, although i'm (or my vassals) in full control of all holdings. Although the tooltip says, i',m missing sth in Volhyina and Kiewan Rus, but actually i'm not?! Have anybody any clues, am i missing sth?
Many thanks in advance!

Steps to reproduce the issue.


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[MesserJoe]

Lol, found it. There was 2 castles, that were independent in my holdings. Don't know when that happend...

 

[RocketRanger]

I had this same problem. For me it was the holy order in my religion that owned these holdings. I had not vassalized the holy order beforehand, and I was unable to vassalize them because their owner's holding was in an independant county. I had to use the decision to expel the holy order (-1000 Piety) to then own all of these holdings. The decision to form the Slavic Union finally had all kingdoms marked as under my control.