Mobile menu does not display

This started happening prior to the most recent update, but the new version also has the problem.

After attempting to add a second button in the header, the mobile/tablet menu will not display. All updated items were removed, but the issue persists.

Clicking on the hamburger menu just displays a blank white page with the hamburger icon instead of the close menu icon that usually replaces it. Have to reload the page to get anything to display.

The page I need help with: [log in to see the link]