Thread:Extension talk:WikiSEO/Page title gets reset after edit, appears again after purge/reply (2)

http://jimbojw.com/wiki/index.php?title=Doing_more_with_MediaWiki_parser_extensions explained why WikiSEO works once and stops working the next time. Basically, when a parser hook is used and parser cache is enabled, whatever in the html body output will be cached (NOT including the meta tags though). So after the purge things will work but when you request it again the meta tags are gone. A quick and dirty (as it disables parser cache) fix is to add $parser->disableCache to be the first line in protected static function processParams($params,$parser){

A proper fix would be to implement something similar to https://www.mediawiki.org/wiki/Extension:Add_HTML_Meta_and_Title, using some tricks to somehow store meta info WITHIN the html body.