Found today, during the final part of RSVP: Polemarch Adrestes (https://www.wowhead.com/quest=61123/rsvp-polemarch-adrestes)
The parangon of Humility, Chyrus, stops saying his lines after calling Adrestes to scold him for not taking the invitation.
He yells “Polemarch Adrestes, attend me please” and then the chat only shows Adrestes replies. Chryrus lines are missing from the chat box and they do not appear on top of his head either.
As per the wow head link, it seems this at least occurred once before on 20-Aug-2022
The quest could still be completed tho