Can you please share admin access details of your site so that I can check the issue on your site with the problem URL. I got the news that there is something related to theme's functions.php file and once I get the access I wanted to verify that.
*** Please make a FULL BACKUP of your database and website.***
I would also eventually need to request temporary access (WP-Admin and FTP) to your site. Preferably to a test site where the problem has been replicated if possible in order to be of better help and check if some configurations might need to be changed.
I have set the next reply to private which means only you and I have access to it.
Based upon the investigation the issue is with your parent theme's functions.php file code. I can see the following code and the issue is coming from that: