DIFF:

$ git diff
diff --git a/course/lib.php b/course/lib.php
index 37c89ebc3e4..9ecf50ba479 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -2508,10 +2508,15 @@ function average_number_of_participants(bool $onlyactive = false, int $lastlogin
         $params['lastlogin'] = $lastloginsince;
     }

+    error_log('count1: ' . print_r($DB->get_field_sql("SELECT COUNT(*) FROM ($sql)", $params), true));
+    error_log('count2: ' . print_r($DB->count_records_sql("SELECT COUNT(*) FROM ($sql)", $params), true));
+    error_log('count3: ' . print_r($DB->count_records_sql("SELECT COUNT(*) FROM ($sql) total", $params), true));
+
     $sql = "SELECT COUNT(*)
               FROM ($sql) total";

     $enrolmenttotal = $DB->count_records_sql($sql, $params);
+    error_log('count4: ' . $enrolmenttotal);

     // Get the number of visible courses (exclude the front page).
     $coursetotal = $DB->count_records('course', ['visible' => 1]);

RESULTS:

count1: 4
count2: 4
count3: 4
count4: 0
F                                                                   1 / 1 (100%)

Time: 00:00.906, Memory: 292.00 MB

There was 1 failure:

1) core_course\courselib_test::test_average_number_of_participants
Failed asserting that 0.0 matches expected 2.