diff --git a/lib/classes/session/manager.php b/lib/classes/session/manager.php
index 250399b8e7c..e370597eb69 100644
--- a/lib/classes/session/manager.php
+++ b/lib/classes/session/manager.php
@@ -689,12 +689,6 @@ class manager {
         global $PERF, $ME, $CFG;
 
         if (self::$sessionactive) {
-            // If debugging, take a snapshot of session at close and compare on shutdown to detect any accidental mutations.
-            if (debugging()) {
-                self::$sessionatclose = (array) $_SESSION['SESSION'];
-                \core_shutdown_manager::register_function('\core\session\manager::check_mutated_closed_session');
-            }
-
             // Grab the time when session lock is released.
             $PERF->sessionlock['released'] = microtime(true);
             if (!empty($PERF->sessionlock['gained'])) {
@@ -704,6 +698,12 @@ class manager {
             self::update_recent_session_locks($PERF->sessionlock);
             self::sessionlock_debugging();
 
+            // If debugging, take a snapshot of session at close and compare on shutdown to detect any accidental mutations.
+            if (debugging()) {
+                self::$sessionatclose = (array) $_SESSION['SESSION'];
+                \core_shutdown_manager::register_function('\core\session\manager::check_mutated_closed_session');
+            }
+
             $requireslock = self::$handler->requires_write_lock();
             if (!$requireslock || !self::$requireslockdebug) {
                 // Compare the array of the earlier session data with the array now, if