The following was reported on phabricator, but was apparently recommended to be brought here too, so here goes (in case anyone has a possible solution):
The magic word {{NUMBEROFACTIVEUSERS}} remains stuck at 0.
This can be seen in Special:Statistics, Special:CreateAccount and wherever the magic word is included in a page.
The Special:ActiveUsers page, however, works fine and lists the active users.
Have already tried unsuccessfully:
initSiteStats.php --update
MediaWiki 1.28.0-alpha (5726c9c) 04:18, 12 July 2016
PHP 5.6.22 (cgi-fcgi)
MySQL 5.6.30-log
ICU 50.1.2
Lua 5.1.5