Aurena - Why isn't my multiselect custom field an option in the search filter drop down menu?

I have a persistent, multiselect custom field in Aurena in the Business Opportunity Screen but it is missing from the search filters that I can choose from at the header level. Normally, when I add custom fields to a screen in Aurena, that field becomes an option as a search filter. Is this restricted to multiselect custom fields or am I missing something? The LU is synced and it is working perfectly in Aurena, I’m just not sure why it isn’t showing up as an option in the search filter drop down.