Menu “undefined” on mobile devices

Hello,
I am trying to fix an error on my customer’s website. Everything works fine on the desktop version, but on a tablet or mobile phone, the top navigation menu says “undefined” when clicked. I searched the issue in the forum and saw that a few people have had this problem. I activated the Enable jQuery Migrate Helper plugin, but that did not solve the issue. Is there anything else that I can do on my end to fix it or does the theme need to be fixed by the eVision Themes?