I noticed some very strange distribution of province and ruler cultures.
Provinces between Rus and Volga river: Mordva, Burtasy, Chuvash, Mountain Cheremisa, Grassland Cheremisa, and Merya. All have Lithuanian culture and Lithuanian rulers.

Should be changed to something more appropriate - unfortunately the closest available culture is Cuman (not perfect, but better than Lithuanian).
Provinces along the Volga: Zyriane, Votyaki, Kama, Bilyar, Bulgar, Syrt, Saray, Lower Volga, and Itil. All have Russian Muslim culture and rulers.

Zyriane and Votyaki have South Slavic Muslim rulers (maybe they were trying to model the Volga Bulgars?). Anyhow, all should be changed to Cuman and/or Mongol.
The Galician provinces: El Bierzo, Santiago, and Compostela. All set to Castillan culture. I would advocate changing to Portuguese, since Galician culture is much closer to Portuguese than to Castillan.
Finally a few words on rulers.
Peter de Maurienne, count of Savoy, has German culture. Should be Frankish or Italian (probably Frankish, at this stage - let his descendants become Italian through the game engine).
Abbasid Caliph is Persian in 1066. Should be Arab, duh.
Most of Seljuq vassals are Arabs, while the Sultan is Turkish. More vassals should probably be Turkish.
Finally, provinces in Persia should have Persian culture.

Let it morph to Turkish naturally through the game events.