Try verifying the integrity of the game files - Right click EU4 in Steam -> Properties -> Local Files -> Verify Integrity... - and relaunch the game.
Make sure that the game has the correct checksum, which is: 78cb (Check in-game, not in the launcher as that always shows the latest correct checksum, not what you actually have)
Make sure that the game has the correct checksum, which is: 78cb (Check in-game, not in the launcher as that always shows the latest correct checksum, not what you actually have)