Hello, Plusout,
Thank you for your response.
We can conclude that the issue is caused by one of the custom functions in your child theme, which start from line 7 and go to the end of the functions.php file, as shown in the screenshot bellow:
https://prnt.sc/XEr9z9-5Eb5E
We have already disabled them on your staging, you need to enable each of them one by one to find out which one is causing the issue.
The file with the functions is located at the following path:
wp-content/themes/xstore-child/functions.php
Kind Regards,
8theme team