I am developing a Central/Peripheral application with SDK 15.2.0 for s132 device on nRF52 development kits. I switch back and forth between my application and the example "ble_app_hrs_rscs_relay" on my nRF52 development boards. In doing so, eventually my nRF52 development boards will throw the error PM_EVT_CONN_SEC_FAILED when running on my application firmware and connecting to a peripheral device. I can never get PM_EVT_CONN_SEC_SUCCEEDED again on this nRF52 development board operating as a Central and Peripheral. When I put my application firmware on a new nRF52 DK, it runs fine and gets PM_EVT_CONN_SEC_SUCCEEDED every time it connects to a peripheral BLE device. This has happened to me with two nRF DKs and now I'm working with a 3rd, but I have not cycled between the "ble_app_hrs_rscs_relay" and my application firmware. I have only been programming it with my application firmware and it has been running fine. I have tried "erase all" on the problem DKs and this didn't help.