With Gerrit change 107988, ActiveUsers is only registered as a special page when $wgMiserMode == false.
This means that when a MiserMode wiki is upgraded to a MediaWiki version that includes this change, Special:ActiveUsers will not be recognised as a special page, and any links to it will become a redlink.
Instead we should show a message such as "This special page is disabled".
Version: 1.23.0
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=60468