Hi @Kenza
Please do a testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Also if you have any custom JavaScripts added on the Theme Options > JS or on specific page JS, try removing it and see if that resolves the issue, if it does then you know its a JS conflict.
Another thing, try switching to parent X theme there might be something on your child theme that causing the issue.
Make sure to do all of this while your caching plugins are cleared and deactivated.
This can also be a server side issue, see to it that your site is in PHP and MYSQL version 5.6 or higher (WordPress requirements) and PHP Memory Limit at least 128MB and PHP Max Script Execute Time to 300, you can use this plugin (https://wordpress.org/plugins/wp-serverinfo/) to check it (under Dashboard > WP-ServerInfo), if one of this is not meet please contact your hosting and ask how you can update/increase it.
If you’re on SiteGround Cloud Hosting, please add this on your .htaccess file located at the root directory of your WP installation.
<IfModule mod_security.c>
SecFilterRemove 001420
</IfModule>
If nothing of this work, please create your own thread and provide us your login credentials there in a “Secure Note”.
(Nope you can not add a secure note here (on someones thread) because it will be visible to the thread starter)
How To Post A Support Question
Cheers!