NRF52 DK won't work well for some bluetooth examples in zephyr project

I choose one NRF52 DK(nrf52840_pca10056) for my daily development. After hundreds of erase and write cycles, the DK won't behaves like it should do. The other DKs runs well while this one not. But some basic example runs well. How can I figure out if this DK is damaged? If so, why is it damaged partially?

what I have tested is, zephyr ibeacon sample works well, while peripheral sample wont work as expected. But other DKs work well.