Cultural Conversion Bug

Hello,

playing Sweboz and conquered southern Britania (Durowernon and Maidunon) but cultural conversion to forest tribalism does not function although I built all buildings for cultural conversion. Especially weird is that I built suebic tribal building showing 2% conversion bonus before building but when ready showing no cultural coversion bonus at all, and buildings from other tribes show conversion bonus in the description when ready but 0%...I guess this is a bug...?!

And even in Sweboz core regions forest tribalism hardly reaches 50 %...in "Denmark" for instance only 34% although I built all buildings available...not very good times for Germanic tribes in EBII...

EDIT: The forest tribalism decreases even in germanic core areas...Cimbri are by only 32%!

Bumped for answers about it