If you use the embed code to embed the iframe code into another activity with a course the embed HTML references two URLs, one for the embed.php file - the URL for this is updated on the backup and restore, and another to h5p-resizer.js - however the resizer scripts URL is not updated. So if you do a backup and then restore to another moodle instance then the URL for the resizer script still references the original courses domain. This is fine if you're restoring a course on the same site, but if you're decommissioning one site and setting up another then the h5p-resizer script will never be served.