In case you are using a mega menu, there is a small chance that it will disappear after we publish a new theme.

The menu is often being dynamically generated by the app called Mega Menu, meaning that every time we/client publishes a new theme live, the Mega Menu would need to be published as well, which can be done in few shorts steps:
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Step 1: Navigate to the Megamenu app and click on the "Add and Design MEGA MENU" button in the bottom right corner.

Step 2: Click on the "Add Mega Menu" button.

Step 3: Select "Main Menu" in the dropdown list and hit the save button

Note: Menu is not always listed as Mega Menu as it depends on how you named it. You can select one from the dropdown menu and see if it's a fit on the left side, if it isn't you can select another one until you find the correct one.