Whenever you have sudden FPS drops/Freezes the best method to fix it is, windows reset. I know it takes a lot of time specially you have to save important files on some external drive. It's honestly the best to resolve all FPS related issues unless you have a potato outdated PC. During windows reset I recommend separating drives specially for FPS/Games in general from program related files.
Also those youtube guides on FPS boost are all bullshit, they don't work. This is the only method that actually works. You can go to nearest computer repair center in your city they'll do the reset with separate drives. This will resolve all you FPS related issues. Along with giving your PC a clean start free of viruses/malwares.