Ok I'm stuck on this one. What could cause the following:

While in the civilopedia, a unit's entry will be blank (like the incorrect art files have been inputed), but if you come back to it later will be complete. Just clicking on the next unit on the list and going right back will fix the problem. See the screenshots.

Does anyone know what's going on here?!?!

Ok I'm stuck on this one. What could cause the following:

While in the civilopedia, a unit's entry will be blank (like the incorrect art files have been inputed), but if you come back to it later will be complete. Just clicking on the next unit on the list and going right back will fix the problem. See the screenshots.

Does anyone know what's going on here?!?!

Did you try to reload the game? This has definitely happened to me before, I just can't remember what I did to fix it...if anything at all. All I remember is that at times when I was first starting to edit LH's in Blender, the LH would appear very "askew" in-game. Sometimes, I would be able to see it in game. Other times, the Civilopedia entry would be blank...like your first screenshot. I had to go back and forth (as you did) several times in order to see it. There might be a problem with the art file that isn't very noticable...but other than that, I'm not sure.

I isolated it almost :) I transplanted techs to older version of 1939 (so the techs, civilizations, and buildings and units doesn't work like net - like it's in bts) and the geme run ok

next the leaders files
CIV4CivilizationInfos.xml
CIV4LeaderHeadInfos.xml
CIV4TraitInfos.xml
CIV4UnitArtStyleTypeInfos.xml
CIV4DiplomacyInfos.xml
CIV4ArtDefines_Civilization.xml
CIV4ArtDefines_Leaderhead.xml

And bang bug in civilopedia and in worldbuilder

OK answer lies here:
CIV4ArtDefines_Leaderhead.xml
CIV4ArtDefines_Civilization.xml

ART_DEF_CIVILIZATION_MINOR
ART_DEF_CIVILIZATION_BARBARIAN
missing in CIV4ArtDefines_Civilization.xml