Hi,
This could be because of a security extension, like RSFirewall, blocking the saving to avoid any potential security issue (since it sees the PHP code of the view arriving in the parameters of the HTTP request.
What you can do is to circumvent that security system:
Once you've used the view builder to move the elements around, the code in the code editor below has been changed accordingly. So you can copy the content there, and then create a file templates/YOUR_TEMPLATE/html/com_hikashop/product/show_default.php and paste that code in there.
That's basically what the "save" button does for you.
Another option would be to disable the security system blocking this. It's not necessarily an extension on your website. It could be a web server module, like mod_security