diff --git a/local/o365/classes/feature/usersync/main.php b/local/o365/classes/feature/usersync/main.php
index 2eee727f5..344f55c29 100644
--- a/local/o365/classes/feature/usersync/main.php
+++ b/local/o365/classes/feature/usersync/main.php
@@ -1310,7 +1310,8 @@ public function sync_users(array $entraidusers = [], string $bindingusernameclai
                      assign.assigned assigned,
                      assign.photoid photoid,
                      assign.photoupdated photoupdated,
-                     obj.id AS objectid
+                     obj.id AS objectid,
+                     obj.objectid AS o365objectid
                 FROM {user} u
            LEFT JOIN {auth_oidc_token} tok ON tok.userid = u.id
            LEFT JOIN {local_o365_connections} conn ON conn.muserid = u.id
@@ -1389,7 +1390,8 @@ public function sync_users(array $entraidusers = [], string $bindingusernameclai
                        assign.assigned assigned,
                        assign.photoid photoid,
                        assign.photoupdated photoupdated,
-                       obj.id AS objectid
+                       obj.id AS objectid,
+                       obj.objectid AS o365objectid
                   FROM {user} u
              LEFT JOIN {auth_oidc_token} tok ON tok.userid = u.id
              LEFT JOIN {local_o365_connections} conn ON conn.muserid = u.id
@@ -1913,13 +1915,22 @@ protected function sync_existing_user(
             }
         }
 
-        // Use pre-fetched O365 object record to avoid N+1 query problem.
-        $localo365objectrecord = $this->o365objectsbymoodleid[$existinguser->muserid] ?? null;
-        if ($localo365objectrecord && $localo365objectrecord->id == $existinguser->objectid) {
-            if ($localo365objectrecord->objectid != $userobjectid) {
-                $localo365objectrecord->objectid = $userobjectid;
-                $DB->update_record('local_o365_objects', $localo365objectrecord);
-                $this->mtrace('Updated user object ID in local_o365_object record.');
+        // The stored Entra ID is usually already available from the existing user query. Fall back to the
+        // pre-fetched object cache (no extra DB query) if this record was built without it, to detect a
+        // changed GUID (e.g. the Entra ID account was deleted and recreated).
+        if (!empty($existinguser->objectid)) {
+            if (isset($existinguser->o365objectid)) {
+                $storedobjectid = $existinguser->o365objectid;
+            } else {
+                $cachedobject = $this->o365objectsbymoodleid[$existinguser->muserid] ?? null;
+                $storedobjectid = $cachedobject->objectid ?? null;
+            }
+
+            if ($storedobjectid != $userobjectid) {
+                $updated = $DB->set_field('local_o365_objects', 'objectid', $userobjectid, ['id' => $existinguser->objectid]);
+                if ($updated) {
+                    $this->mtrace('Updated user object ID in local_o365_objects record.');
+                }
             }
         }
 
diff --git a/local/o365/classes/task/forcefullusersync.php b/local/o365/classes/task/forcefullusersync.php
new file mode 100644
index 000000000..474e4fa09
--- /dev/null
+++ b/local/o365/classes/task/forcefullusersync.php
@@ -0,0 +1,71 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * An adhoc task to force a one-off full Microsoft Entra ID user sync.
+ *
+ * @package     local_o365
+ * @author      Lai Wei <lai.wei@enovation.ie>
+ * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @copyright   (C) 2026 onwards Microsoft, Inc. (http://microsoft.com/)
+ */
+
+namespace local_o365\task;
+
+use core\task\adhoc_task;
+use local_o365\feature\usersync\main;
+
+/**
+ * Adhoc task to force a one-off full Microsoft Entra ID user sync.
+ *
+ * Queued during upgrade to repair Moodle accounts whose linked Microsoft Entra ID object ID
+ * went stale (e.g. the Entra ID account was deleted and recreated more than 30 days ago) before
+ * the fix to the object ID repair logic in the user sync task. Delta sync only reports users
+ * that changed since the last sync, so accounts that were already stale before this fix would
+ * not otherwise be picked up again on their own. If the site currently uses delta sync, this
+ * temporarily enables a full sync for a single run, then restores the previous setting. If a
+ * full sync already runs every time, no override is needed.
+ */
+class forcefullusersync extends adhoc_task {
+    /**
+     * Execute the task.
+     *
+     * @return bool
+     */
+    public function execute(): bool {
+        if (main::sync_option_enabled('nodelta')) {
+            mtrace('Full sync already runs every time (nodelta enabled). No override needed.');
+
+            return true;
+        }
+
+        $originalsetting = (string) get_config('local_o365', 'usersync');
+        $originaloptions = array_filter(explode(',', $originalsetting));
+
+        mtrace('Delta sync is currently in use. Temporarily forcing a full sync for this run...');
+        set_config('usersync', implode(',', array_merge($originaloptions, ['nodelta'])), 'local_o365');
+
+        try {
+            $task = new usersync();
+            $task->execute();
+        } finally {
+            set_config('usersync', implode(',', $originaloptions), 'local_o365');
+            mtrace('Restored previous delta sync setting.');
+        }
+
+        return true;
+    }
+}
diff --git a/local/o365/db/upgrade.php b/local/o365/db/upgrade.php
index d351f250c..d027fd18a 100644
--- a/local/o365/db/upgrade.php
+++ b/local/o365/db/upgrade.php
@@ -1641,5 +1641,22 @@ function xmldb_local_o365_upgrade($oldversion) {
         upgrade_plugin_savepoint(true, 2025100600.03, 'local', 'o365');
     }
 
+    if ($oldversion < 2026042000.04) {
+        // Queue adhoc task to force a one-off full user sync, repairing accounts whose linked
+        // Microsoft Entra ID object ID went stale (e.g. the Entra ID account was deleted and
+        // recreated) before the object ID repair logic in the user sync task was fixed. Delta
+        // sync only reports users that changed since the last sync, so already-stale accounts
+        // would not otherwise be picked up again on their own.
+        $task = new \local_o365\task\forcefullusersync();
+        // Set next run time to ensure it runs in the next cron cycle, not during upgrade.
+        $task->set_next_run_time(time() + 60);
+        \core\task\manager::queue_adhoc_task($task);
+
+        mtrace('Queued adhoc task to force a full user sync and repair stale Entra ID object IDs.');
+
+        // O365 savepoint reached.
+        upgrade_plugin_savepoint(true, 2026042000.04, 'local', 'o365');
+    }
+
     return true;
 }
diff --git a/local/o365/version.php b/local/o365/version.php
index 33ebbe24e..15bac6d7a 100644
--- a/local/o365/version.php
+++ b/local/o365/version.php
@@ -26,7 +26,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version = 2026042000;
+$plugin->version = 2026042000.04;
 $plugin->requires = 2026042000;
 $plugin->release = '5.2.0';
 $plugin->component = 'local_o365';