[UPDATE] WPML has released a new version with a permanent fix, download version 3.8.4 from wpml.org.
BREAKING NEWS … Literally!
If you experience inexplicable 404s on your WordPress site after you updated to version 4.8.3, and you are using WPML (sitepress multilingual cms) version 3.8.0 or higher, you will need a fix. (Duh!)
The cause is WPML
not properly using WPDB->prepare(); [UPDATE] is too late with adding/removing the filters on the query. The priority is now fixed from 10 to -1.