If your main menu displays on desktop and laptop devices, but not on mobile devices, this may be due to not having a menu assigned to the main menu location. To solve this issue, you must ensure a menu is assigned. To learn more about this, please continue reading below.
Step 1 – Navigate to the WordPress Dashboard > Appearance > Menus > Manage Locations section
Step 2 – Ensure that the Main Navigation is assigned under Theme Location > Assigned Menu
Cache us often a culprit with issues like this. If you are running any cache plugins on your website, make sure that you clear your cache as well as clearing your browser/device cache when checking on mobile.
If you have purged your cache and ensured that the main menu is assigned in the WordPress menu section, then you need to check for 3rd party plugin conflicts. Go to WordPress Dashboard > Plugins and disable all 3rd party plugins (except the Fusion Core and Fusion Builder) and then re-enable them one by one until you find the culprit.