Geocortex Basemap Switcher and Transparency Group Error

I’m setting up a basemap switcher for a test HTML5 viewer. I have set up a transparency slider group for our imagery to slide between imagery years.  

 

This works. But when I go to try to set the visibility behaviour of the folder of map services to “Only One Visible at a Time” the basemap toggler does not show in my viewer. No errors appear in the browser console.

 

The steps I am taking are as per Geocortex Essentials 4.4.3 Admin Guide PDF p83-84.  I’d like it to snap to an image as described in the docs.

 

I created an animated gif of the behaviour but its too large for this forum.