i allways et this error report when event forcing changin of region ovnership to another :
18:06:05 TRegionCmns.OnCaptureSupply No exclusive structure owner or owner is not an enemy in Region: 156 Gaining Faction: Austria
this problem fire even is everthing seems ok in event - "robbed" owner is same in game as in event and new one dont recive that region.
when manualy i fired this earlier - in polish uprising and help from austria, when they correctly given me back regions from rebels, but keeped town/industrys, i got them back - mazovia and left from it, i get all back except one small problem - cant build military units here, but in all other regions in poland normaly.