Alright that it good to know,
First of all try to right click on your game on steam and select properties and go to the 'updates' tab make sure it says 'always keep this game up to date' where it says automatic updates. If that option is not selected try to select it. If you struggling to locate that, please try to find how to on YouTube / or even google. CHECK if this updated your game.
Before trying the second method, please make sure you make a copy of your saves and all plugins as I am not sure if it could delete them.Second method : Again go to the Properties but this time go to the Local files tab. Now go do the verify the integrity of game files.This scans your game and adds on all files you might be missing. Try CHECKING if the game updated again.
Please reply if this worked for you ( if it did great job) and if it did not you can try to look for other option on the internet HOWEVER please always make a copy of your saves files and plugins so you can retrieve them easily if anything goes wrong
Another option is just to try to reinstall the game however you can try the other methods first.
Good luck.