There seems to be a conflict with WordPress 4.9 and Yoast, on one of my sites I uploaded a a back up of a WordPress 4.8.3 which fixed the issue, but then it attempted to auto update to 4.9 which crashed the site and I had to disable Yoast to get back into the site. I don’t know if there’s an issue that’s currently being looked at as this has happened to 5 of my sites.
