As you’ll see in my link, the field is displaying properly for me when I use it in the default BuddyBoss Profile field. (The fieldset labeled ‘Details’) It’s not displaying when I use it in a new field set. (In my case, the fieldset labeled ‘Recent Experiences’)
Could you try using the field in a new fieldset and see if it works for you?
Under the “Profile” tab I have a subnav called “Recent Experiences”. In the “Recent Experiences” subnav I have a field called “Production Title”. In the “Production Title” field I am using the field “Custom Taxonomy Multiselector”. You can see how I have the field set up here: https://crewcall.community/wp-content/uploads/2021/04/no_show_field01.jpg
When I edit my profile on the frontend this is the result. https://crewcall.community/wp-content/uploads/2021/04/no_show_field02.jpg