Item Tags label menu doesn't drop down in Holdings Editor

Evergreen 3.9.1

When adding an item tag to an item via the holdings editor there is a field for entering the tag label where you can add free text or select from pre-existing tag labels.

In 3.9.1 the field has arrows indicating that you should be able to see a list of the pre-existing tag labels but clicking on the arrows does nothing. If you start typing in the field matching values will display in a drop down.

The list of pre-existing labels should display when you click in the field or on the arrows as it does for other fields.