Farakka used to be a late runner and slacker, that's the reason that despite getting confirmed seats everytime, I never preferred it even over other highly WL options.
But that being said, 12 hours? That's too much. That's basically harassing the passangers. And I don't think until BLGT CDO is fully functional this issue is going anywhere. Even after that, it'd take them months or years to operate this smoothly with spares, and timely repairs.