Does it only affect a specific save or also happens in a new campaign?
If it happens in a new campaign, does it help if you disable all mods(if you think that you have no mods, look in the playset section of the launcher to make sure, because they might have been installed and activated without your knowledge)?
If it happens in a specific save, are you using mods? If you are using mods, please ask the mod authors for help(if you use more than one game changing mod, you are the author of that combination unless all mods explicitly guarantee compatibility with each other). If you don't use any mods, can you attach your save here?
Disclaimer: I'm not working for Paradox. I'm just trying to help people.