Error saving custom patterns and template parts in WP 6.6

The site editor in WordPress 6.6 is given an error when trying to save a custom pattern o template part.

TypeError: Cannot read properties of undefined (reading 'form')
    at e.<computed>.valid (jquery.validate.js?ver=1.20.0:131:29)
    at editor.savePost (validation.js?ver=5.9.10:239:21)
    at Object.savePostStatus (editor.min.js?ver=734dedd6ead28ee4ca9c:7:150370)
    at data.min.js?ver=7c62e39de0308c73d50c:9:3735
    at editor.min.js?ver=734dedd6ead28ee4ca9c:7:149054
    at editor.min.js?ver=734dedd6ead28ee4ca9c:7:148202
    at n.<computed> (components.min.js?ver=36b97398bf090476214e:27:14952)
    at Object.De (react-dom.min.js?ver=18.3.1:2:16716)
    at Be (react-dom.min.js?ver=18.3.1:2:16870)
    at react-dom.min.js?ver=18.3.1:2:36731

jquery.validate.js?ver=1.20.0:131:29

Steps to reproduce:

1. Install or update to WordPress 6.6-RC3
2. Install and activate meta-box plugin (5.9.10)
3. Register custom meta-box field in functions.php
4. Add a new Pattern o Template Part from the Site Editor
5. Edit the contents of the created pattern and try to saved.

<?php // theme/functions.php

add_filter( 'rwmb_meta_boxes', function ( $meta_boxes ) {
? $meta_boxes[] = [
? ? 'title' ? ?=> 'Event details',
? ? 'post_types' => 'page',
? ? 'fields' ? => [
? ? ? [
? ? ? ? 'name' => 'Location',
? ? ? ? 'id' ? => 'location',
? ? ? ? 'type' => 'text',
? ? ? ],
? ? ],
? ];
? return $meta_boxes;
} );