sd_softdevice_enable hangs on nRF51822 when running example ble_app_hrs

[Red Shaya]

I'm using SDK 11.0 and example\ble_central\ble_app_hrs_c

I have cut SB1 SB2 to disconnect the 32Khz crystal from the pca10028 and configured the example program to use the NRF_CLOCK_LF_SRC_RC. When loading the application on the pca10028 the sd_softdevice_enable ruturns with NRF_SUCCESS

When I try to load the same application on my custom board (with nRF51822) with 16Mhz crystal (no 32Khz crystal) the sd_softdevice_enable never returns.