I recently installed MediaWiki for a group I'm affiliated with: http://wiki.vvfh.org.
When I enabled the Publish/Cancel buttons, I discovered that the Cancel button returns an undefined error. The Publish button works as expected
See this discussion for details: https://www.mediawiki.org/w/index.php?title=Topic:Tzak3kzab3w3cfc0&fromnotif=1#flow-post-tzbcevfsuccaxe68
This is browser-displayed error. The error is not browser-dependent. (I've tested it in Safari, Chrome and Edge.)
The requested URL /undefined was not found on this server.
This is my system software:
PHP 7.1.9 (apache2handler)
I have it disabled until I can resolve this.