Apple Music / Roku Voice Control Previous Command

When using the Apple Music app on Roku (Ultra 4802R), saying "previous" or "back" (or anything to that effect) doesn't work - I get a "Sorry I didn't understand" message.  Saying next works fine, but previous does not.  I know you can use the remote to do this, but trying to accomplish via the hands-free "hey roku" route.  

Thanks for any insight!