Autocomplete's dependencies are not resolving and are leaving the CSS in a broken state.

Attempting to include only autocomplete widget: application.js has //= require jquery-ui/widgets/autocomplete and application.css.scss has *= require jquery-ui/autocomplete results in

And the ui-helper-hidden-accessible div is visible.

If you include all of jquery-ui in those files it instead looks like this and ui-helper-hidden-accessible div is hidden.

Functionality seems to work fine, so it may be a CSS only problem