It actually is WP Fastest Cache. I’ve been having the same issues for a couple months. The way to temporarily get your site back up is to go to your permalink settings. You’ll see 6 different “Common Settings”. Change to anything other than what it’s currently on and save it at the bottom. Then go back and change it back to the way you had it and re-save it. I’ve been doing this for 2 months thinking it was a malware issue. I just spoke to my hosting provider and their support team just figured out that WP Fastest Cashe rewrites the file that controls the permalinks, which causes the 404 error.
