Hello Francisco,
Can You please try adding the following to your site’s .htaccess file to get it to work:
<IfModule mod_security.c>
SecFilterRemove 001868
</IfModule>
Or, you also may contact hosting support.
However, Your server is blocking the HTML data request as well like this. That’s why the saving button kept rolling. It’s working perfectly on other servers. So, if your server keeps blocking the HTML data then the setting will not save and it will keep spinning.
Hope you understand.
Thanks