I partly have this problem: Manual:Errors and symptoms#All pages have no content, but when editing a page the wiki text is there
The solution mentioned is upgrading to a supported mediawiki version but this occurred after the upgrade to 1.31
But its a bit vague because some parts can be seen on the page but the majority can not. The language bar, categories and a Infobox template are viewable but the rest of the page content is not. It is also not on all pages, just on some.
All googling just directs me to the error I mentioned earlier. Any help would be appreciated.