I was running MediaWiki on Apache with mod_php, but I switched over to php-fpm on nginx.
--> https://www.nginx.com/resources/wiki/start/topics/recipes/mediawiki/
The preview works successfully, but actually saving an edit causes a 404 not found error to be reported by nginx. I am wondering if something might be deadlocked in the database, and the fastcgi_pass to php-fpm is not producing any output.
No permanent damage, because it is possible to reload the page or navigate back to it, and find that one's edits were in fact saved.
Otherwise, php-fpm on nginx seems to be somewhat faster and use less resources than the "standard" Apache/mod_php solution.