A few months ago, Special:Nuke started taking a very long time to open (as in, 20 seconds or so).
For some users it times out altogether. I just tried to hit https://commons.wikimedia.org/wiki/Special:Nuke/MathewMunro and it failed with the following text.
Perhaps someone incorrectly removed a database index?
MediaWiki internal error.
Original exception: [W1OcggpAICsAAL8xAnQAAACS] 2018-07-21 20:51:11: Fatal exception of type "Wikimedia\Rdbms\DBQueryTimeoutError"
Exception caught inside exception handler.
Set $wgShowExceptionDetails = true; and $wgShowDBErrorBacktrace = true; at the bottom of LocalSettings.php to show detailed debugging information.