Customize Menu Titles not working [#2844256]

I'm working with an AT subtheme that I built three years ago. The debugging function shows that it is compatible with AT 7.x-3.x, and I have AT Core 7.x-3.4+1-dev enabled on the site.

I have enabled the mobile menu toggle extension, using the Main Menu in its default location, where it is output in the page template. Superfish is on the site but the module is presently disabled.

I am trying to change the label of the toggle link from Main Menu to Menu, using the Customize Menu Titles field. Have tried clearing the cache several times, but it does not change.

Thinking I might need to add something to the subtheme to make this work on account of the fact that it is three years old, but not sure.