Jul 21 2019
It seems that George Reeves Person entered Jimbo Wales' Wikimedia email address multiple times creating a bunch of tickets. Please see #2019072010004768, #2019072010004741, and 16 others.
Jul 24 2017
Dec 29 2016
Jul 25 2016
Happened on Special:Undelete as well when trying to view a deleted article.
Jul 21 2016
Happened to me a few minutes ago when attempting to block a user at the same time as another administrator completed the action. Page should have been a block conflict one.
Sep 30 2015
Happened to me on Simple Wikipedia and Mediawiki.org