The menu item describes pretty much exactly what the problem is: the page has no title.
If I create a new page, don’t give it a title, and then add it to the menu, this is exactly what happens:
My menu items are “Pages” (not custom) and have a Navigation Label entered. Screenshot.
The WP Page edit screen has the relevant page title in the appropriate place. Screenshot.
As mentioned, the strange thing is that it’s only happening on ACTIVE pages. E.g., when visiting the About page (I.e., sitename.test/about) the nav menu label shows the Page ID + (no title) (I.e., “#166 (no title)”). When loading ANY other page, the nav menu label loads as you would expect (E.g., “About”)
I’ve solved this issue. The problem was a filter added to the child theme to hide the default page title. The issue was fixed when I added and modified the Bricks specific filter and it’s working as expected.