Thanks for asking.
I checked the website link you have shared (http://www.shai.com.mx/) and I see that you are using in-compatible version of X Theme and Cornerstone i.e X Theme 5.1.0 and Cornerstone 3.1.6 (screenshot in secure note). That might be the reason why mobile menu is not working. I would suggest you to copy the website on a staging server and update Cornerstone and X Theme over there to the latest version. We have released X Theme version 6.2.1 and Cornerstone version 3.2.1. After updating see how mobile menu behaves. In case any issue comes up the same can be worked on without effecting the live website.
To update Cornerstone and X Theme please take a look at following resources:
Version compatibility guide: To learn about the latest and compatible versions of bundled and supported plugins, please take a look at following doc:
2. Theme Update guide: Please take a look at following article to update Cornerstone.
3. Please take a look at following doc about changelog: