Originally posted by EssoBunny:

1. Clear cache
2. Resubscribe to rt56
3. Delete the mod_registry.json file and the mod file located in documents/Paradox Interactive/hoi4 (I personally don't use this method because whenever I tried to do it, it just broke all of my mods, but it might work for you)
4. Verify the integrity of your game files
5. Do a quick and normal reinstall of the game (As in just press uninstall and then reinstall)
6. If all else fails, a clean reinstall of the game will fix all of your problems 99% of the time. It's a pain in the butt to do if you're doing it for the first time since you have to uninstall all of your mods, but it really does fix everything. But before you do unsubscribe from all of your mods, make sure to either favorite all of them or compile them into a collection. (Here's a guide on how to do the clean reinstall: https://kaiserreich.fandom.com/wiki/How_to_do_a_Clean_Install)