Steps to replicate the issue (include links if applicable):

• Run a normal wiki with $wgMiserMode = false;
• Note that {{ACTIVEUSERS}} and the count on Special:Createaccount and Special:Statistics just gets further and further out of date

What happens?:

The active user count is never updated

What should have happened instead?:

There should be some mechanism to update the count when $wgMiserMode = false; The general expectation is you only need to run updateSpecialPages.php if you have $wgMiserMode = true;

Probably one of two things should happen:

• Since we are not in miser mode and don't care about hurting the DB, we should just dynamically calculate it each time with some caching, just like numberingroup
• We should recalculate it as part of the RecentChange update job that updates Special:ActiveUsers

This is a regression of T17666: "Active users" count invalid if updateSpecialPages hasn't been run

Software version (skip for WMF-hosted wikis like Wikipedia):

master