diff --git a/openedx/core/djangoapps/content_libraries/api/collections.py b/openedx/core/djangoapps/content_libraries/api/collections.py
index 9d011bdae363..962f2c840c42 100644
--- a/openedx/core/djangoapps/content_libraries/api/collections.py
+++ b/openedx/core/djangoapps/content_libraries/api/collections.py
@@ -176,6 +176,26 @@ def update_library_collection_items(
             created_by=created_by,
         )
 
+    # Explicitly emit LIBRARY_COLLECTION_UPDATED with background=True after the
+    # M2M relationship has been committed. The post_save signal on Collection
+    # fires before the entities M2M commit, so its synchronous reindex would
+    # see a stale num_children. The async (background) reindex runs after the
+    # request transaction commits and computes the correct count. This mirrors
+    # the pattern already used by set_library_item_collections,
+    # delete_library_block, restore_library_block, delete_container, and
+    # restore_container. See bug #35776.
+    # .. event_implemented_name: LIBRARY_COLLECTION_UPDATED
+    # .. event_type: org.openedx.content_authoring.content_library.collection.updated.v1
+    LIBRARY_COLLECTION_UPDATED.send_event(
+        library_collection=LibraryCollectionData(
+            collection_key=library_collection_locator(
+                library_key=library_key,
+                collection_key=collection.key,
+            ),
+            background=True,
+        )
+    )
+
     return collection
 
 
diff --git a/openedx/core/djangoapps/content_libraries/rest_api/collections.py b/openedx/core/djangoapps/content_libraries/rest_api/collections.py
index 3f67f5e777a8..82218e74d915 100644
--- a/openedx/core/djangoapps/content_libraries/rest_api/collections.py
+++ b/openedx/core/djangoapps/content_libraries/rest_api/collections.py
@@ -5,6 +5,7 @@
 
 from django.db import transaction
 from django.db.models import QuerySet
+from django.utils.decorators import method_decorator
 from django.utils.text import slugify
 from opaque_keys.edx.locator import LibraryLocatorV2
 from openedx_authz.constants import permissions as authz_permissions
@@ -27,6 +28,10 @@
 from .utils import convert_exceptions
 
 
+# LibraryCollectionsView must run outside the per-request atomic transaction so
+# that LIBRARY_COLLECTION_UPDATED tasks enqueued from update_library_collection_items
+# land after the M2M commit. See bug #35776.
+@method_decorator(transaction.non_atomic_requests, name="dispatch")
 class LibraryCollectionsView(ModelViewSet):
     """
     Views to get, create and update Library Collections.
diff --git a/openedx/core/djangoapps/content_libraries/tests/test_api.py b/openedx/core/djangoapps/content_libraries/tests/test_api.py
index a6528c089bd0..6880361f6c99 100644
--- a/openedx/core/djangoapps/content_libraries/tests/test_api.py
+++ b/openedx/core/djangoapps/content_libraries/tests/test_api.py
@@ -250,7 +250,11 @@ def test_update_library_collection_components_event(self) -> None:
             ],
         )
 
-        assert event_receiver.call_count == 4
+        # 3 CONTENT_OBJECT_ASSOCIATIONS_CHANGED (per entity) + 1 implicit
+        # LIBRARY_COLLECTION_UPDATED from Collection.post_save +
+        # 1 explicit LIBRARY_COLLECTION_UPDATED with background=True emitted
+        # after the M2M commit (bug #35776).
+        assert event_receiver.call_count == 5
         self.assertDictContainsEntries(
             event_receiver.call_args_list[0].kwargs,
             {
@@ -297,6 +301,65 @@ def test_update_library_collection_components_event(self) -> None:
                 ),
             },
         )
+        # Regression for bug #35776: explicit background=True emit after M2M commit.
+        final_call = event_receiver.call_args_list[4].kwargs
+        assert final_call["signal"] == LIBRARY_COLLECTION_UPDATED
+        assert final_call["library_collection"] == LibraryCollectionData(
+            collection_key=api.library_collection_locator(
+                self.lib1.library_key,
+                collection_key="COL1",
+            ),
+            background=True,
+        )
+
+    def test_bug_35776_regression_update_items_emits_background_updated(self) -> None:
+        """
+        Regression for bug #35776: update_library_collection_items must emit
+        LIBRARY_COLLECTION_UPDATED with background=True after the M2M commit
+        so the async reindex sees the final count. Without this, the search
+        document num_children reflected the stale pre-M2M state.
+        """
+        collection_update_event_receiver = mock.Mock()
+        LIBRARY_COLLECTION_UPDATED.connect(collection_update_event_receiver)
+
+        api.update_library_collection_items(
+            self.lib1.library_key,
+            self.col1.key,
+            opaque_keys=[
+                LibraryUsageLocatorV2.from_string(self.lib1_problem_block["id"]),
+                LibraryUsageLocatorV2.from_string(self.lib1_html_block["id"]),
+            ],
+        )
+        background_emits = [
+            call.kwargs for call in collection_update_event_receiver.call_args_list
+            if call.kwargs.get("library_collection")
+            and call.kwargs["library_collection"].background is True
+        ]
+        assert len(background_emits) >= 1
+        assert background_emits[-1]["library_collection"] == LibraryCollectionData(
+            collection_key=api.library_collection_locator(
+                self.lib1.library_key,
+                collection_key="COL1",
+            ),
+            background=True,
+        )
+
+        # Also fires for removals
+        collection_update_event_receiver.reset_mock()
+        api.update_library_collection_items(
+            self.lib1.library_key,
+            self.col1.key,
+            opaque_keys=[
+                LibraryUsageLocatorV2.from_string(self.lib1_html_block["id"]),
+            ],
+            remove=True,
+        )
+        background_emits = [
+            call.kwargs for call in collection_update_event_receiver.call_args_list
+            if call.kwargs.get("library_collection")
+            and call.kwargs["library_collection"].background is True
+        ]
+        assert len(background_emits) >= 1
 
     def test_update_collection_components_from_wrong_library(self) -> None:
         with self.assertRaises(api.ContentLibraryBlockNotFound) as exc:  # noqa: PT027