It could be that card can't handle the same overclock as the others, causing it to hang from memory errors. I have cards with Hynix memory that have a 1500 MHz strap mod and are fine with a 2075 MHz overclock. Other cards with the same memory I can only go up to 2020 MHz before there are memory errors. Try reducing the core 10 MHz and the memory by 50 Mhz on the card that's crashing and see if it helps. It could also be from undervolting too much.