Listbox autocomplete not working

I have an application with a main container that covers the entire window. I have a container on top of that for Sessions, and a container on top of that for Exposures:

maincontainer - session container - exposure container
depending on user input, the session container is visible and the exposure container is not - or reversed as expected.

The listboxes on the session container work with autocomplete.
The listboxes on the exposure container do not work. In fact they are not enabled and cannot be accessed.

I’ve checked the container and listbox properties and see no differences.

Any help would be appreciated.