Will not play certain discs in a box set but will play others?

Hello, so I have these DVD discs in a full box set, and I recently got half the way through, and after that, all of the discs stopped working, and it was an equal half that worked and an equal half that didn't work, but not all one after the other, it was in a mixed order. I've searched everywhere for answers but I'm so stuck for why! We've analysed the discs and everything seems to be in order, and have also tried it on another blu ray device and pc. The DVD was the beavis and butthead Mike judge collection, and this hasn't happened before with my other beavis and butthead dvds. Thanks!!