Thanks for asking.
Menu is not working in mobile view is because you are using incompatible version of X Theme and Cornerstone. As you have updated Cornerstone, please update X Theme as well from 4.6.4 to version 6.3.8.
Please update X Theme and that should fix the problem of mobile menu you are facing. As you are going to update fairly old version of X Theme, you will have to manually update the same. Before doing any changes, please take a complete site backup. To be on the safer side, I suggest you to create a staging server and copy the website over there to test the update process. In case any issue comes up the same can be looked at without affecting live website. Here's some resources to help you:
1. Backup: https://fizzle.co/sparkline/backup-wordpress
2. Staging server: https://www.shoutmeloud.com/wordpress-staging-site-server-testing.html
1. Manual Update:
Please take a look at following article and scroll down to Manual Update section on instructions to manually update Theme:
To help you get started, you can follow below instructions also:
Manual X Update Via FTP
- Unzip x.zip on your computer.
- Rename the x folder to x-updating.
- Connect to your server via FTP and navigate to your /wp-content/themes/ directory.
- Drag and drop the x-updating folder into your themes directory.
- Upon completion, rename the previous x folder to x-previous.
- Rename x-updating to x. Your site will now be at the latest version.
- Delete the x-previous folder.
- Visit the WordPress dashboard at least once to ensure any migration logic can run (this happens behind the scenes).
Please note that you will need FTP softwares like Filezilla to manually upload the files. Here's a getting started guide that you can take a look.
Let us know how it goes.