I have tried running the ble_app_uart project on nrf51 DK. Initially the program compiled and ran perfectly(I was able to see that device on nrf UART app). Later when I used the nrf51 DK to program nrf51822 on a custom PCB I was able to make the blinky project work. However when I tried to program the ble_app_uart project again on the PCb and nrf51DK it compiles and programs but I am unable to see the device on the nrf UART app.
TLDR- ble_app_uart worked on the nrf51DK. Later I try to use nrfDK to program ble-app_uart on nrf51822 on PCB it stops working on both the DK and PCB. Blinky LED stil works on both.