I have a few of the chip that you show with the cracks (the Ladbrokes Piccadilly 20p) and none have that sort of damage - in fact I don't think any of my chips do. I can only imagine either extreme conditions (heat or cold) would cause that, especially if you have several like that.

Let me know if you want another one of those chips and I'll send you one out (I just need your address)

Regards

Jason