Cannot exit horizontal drop-down menu using accessibility tools

We've conducted some accessibility testing on our wiki site and noticed an issue with the horizontal menu. 

As reported by our tester: 

Dropdown menus, when presented via keyboard focus, cannot be dismissed via Esc key, and can only be dismissed by mouse. This is problematic as the dropdown menus cover important content on the site (breadcrumb menu), and may interfere with the user’s ability to do a task or access content without dismissing the popup.

This results in a fail for WCAG 2.1 Success Criterion 1.4.13 Content on Hover or Focus. 

Tested with:

Browser/OS: Google Chrome/Windows
Screen Reader: NVDA