The game itself has not changed in that time, so it must be an installation corruption or something else on your computer doing this.
I assume HOI4, Stellaris and EU4 are unaffected by this, or you would have mentioned?
Please do a full **clean** re-install:
- move any valued save games elsewhere
- "uninstall" in Steam-CK2
- manually delete both the Steam/SteamApps/common/CK2 AND Documents/Paradox/CK2 folders
- re-install game in Steam, run a Steam Verify when done.
- start the game with no mods active and test
In particular make sure there are no files or folders left under either the Steam CK2 or Documents CK2 locations, before installing again.