The stats_cron_daily() function in the file lib/statslib.php is checking for the existance of the functions $mod->name."_get_daily_stats" (line 85) and then building an array containing those function names. The problem is that for all of the Moodle modules, these functions do not exist so an empty array of function names (which are supposed to be executed by the cron job) are being passed to the function stats_do_daily_user_cron().

The end result is that the cron job is running successfully, but no actual process of statistics is taking place and the mdl_stats_daily table in the database is remaining empty.