Thanks for your reply it turned out to be the beaver builder plugin clearing it’s cache.
When BB clears it’s cache our sites always get 404s on files from /wp-content/uploads/bb-plugin/cache.
Purging the litespeed cache solves it. Unfortunately updating the version of bb also causes it to do a cache clear the next time the back end is loaded. So the sites will always break eventually once they are logged in. (if litespeed is not purged at the same time)