Index: src/wp-admin/includes/ajax-actions.php
===================================================================
--- src/wp-admin/includes/ajax-actions.php	(revision 35773)
+++ src/wp-admin/includes/ajax-actions.php	(working copy)
@@ -2376,7 +2376,7 @@
 	$query = new WP_Query( $query );
 
 	$posts = array_map( 'wp_prepare_attachment_for_js', $query->posts );
-	$posts = array_filter( $posts );
+	$posts = array_values( array_filter( $posts ) );
 
 	wp_send_json_success( $posts );
 }