If you added the Panelist as a Panelist though the Dashboard before the webinar was started, then the Join link they got in an email should be a Panelist Join Link, and they should enter the webinar as a panelist. Is it possible these folks ignored the Panelist Join Link and registered for the webinar as a regular Attendee?
BTW - I never do this. I have had bad experiences with Panelists sharing their Join Link, thus enabling multiple people who should be Attendees to join the same webinar as Panelist.
I have all of my presenters join as an Attendee, then within the webinar, I promote them to be a Panelist. This works best for me.