I've done that encounter on 7 separate occasions without any technical issues. Sure, it can be annoying if you get into a failed save loop, but at least one character will eventually snap out of it to progress the fight, and none of the harpies have ever gone anywhere that was out of reach, nor sing indefinitely. Not entirely clear on how you "lost two hours of play" either.

I don't want to fall to bits 'cos of excess existential thought.