sub-menu navigation doesn’t work on Lumia 550 running Windows 10 Mobile

With Navigation Dropdown set to Hover, the navigation works correctly on desktop and most mobile devices. However, the site owner has a Lumia 550 2.0.1.0 running Windows 10 Mobile version 1703, OS build 10.0.15063.483. On this device, the sub-menu can be opened by tapping, but tapping on a sub-menu item closes the menu without navigating to the chosen page.

With Navigation Dropdown set to Click – Menu Item, navigation works correctly on the Lumia 550, but the site owner does not want to force the extra click on desktop.

I haven’t been able to test the site on any other physical devices running Windows 10 Mobile. The emulators I tried don’t show the problem.