Weird disconnection issues with ble_app_hrs example from SDK 15

Question

For some reason the ble_app_hrs example from SDK 15 disconnects after around 30-40 seconds (every time) and shows this error in the RTT logger: " 0> <info> app: Disconnected, reason 34."

However, it does not happen with the ble_app_hrs example from SDK 12.3.

The only changes I made to both examples is set the internal LF clock source to RC because my custom PCB does not have external 32 KHz clock.

In the ble_app_hrs from SDK 15 I did this:

#ifndef NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 0
#endif

// <o> NRF_SDH_CLOCK_LF_RC_CTIV - SoftDevice calibration timer interval. 
#ifndef NRF_SDH_CLOCK_LF_RC_CTIV
#define NRF_SDH_CLOCK_LF_RC_CTIV 16
#endif

// <o> NRF_SDH_CLOCK_LF_RC_TEMP_CTIV - SoftDevice calibration timer interval under constant temperature. 
// <i> How often (in number of calibration intervals) the RC oscillator shall be calibrated
// <i> if the temperature has not changed.

#ifndef NRF_SDH_CLOCK_LF_RC_TEMP_CTIV
#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 2
#endif

// <o> NRF_SDH_CLOCK_LF_ACCURACY - External clock accuracy used in the LL to compute timing.
 
// <0=> NRF_CLOCK_LF_ACCURACY_250_PPM 
// <1=> NRF_CLOCK_LF_ACCURACY_500_PPM 
// <2=> NRF_CLOCK_LF_ACCURACY_150_PPM 
// <3=> NRF_CLOCK_LF_ACCURACY_100_PPM 
// <4=> NRF_CLOCK_LF_ACCURACY_75_PPM 
// <5=> NRF_CLOCK_LF_ACCURACY_50_PPM 
// <6=> NRF_CLOCK_LF_ACCURACY_30_PPM 
// <7=> NRF_CLOCK_LF_ACCURACY_20_PPM 
// <8=> NRF_CLOCK_LF_ACCURACY_10_PPM 
// <9=> NRF_CLOCK_LF_ACCURACY_5_PPM 
// <10=> NRF_CLOCK_LF_ACCURACY_2_PPM 
// <11=> NRF_CLOCK_LF_ACCURACY_1_PPM 

#ifndef NRF_SDH_CLOCK_LF_ACCURACY
#define NRF_SDH_CLOCK_LF_ACCURACY 1
#endif

And in the ble_app_hrs from SDK 12.3 I added 3 lines to ble_stack_init():

static void ble_stack_init(void)
{
 uint32_t err_code;

 nrf_clock_lf_cfg_t clock_lf_cfg = NRF_CLOCK_LFCLKSRC;

 clock_lf_cfg.source = 0;
 clock_lf_cfg.rc_ctiv = 16;
 clock_lf_cfg.rc_temp_ctiv = 2;
 //clock_lf_cfg.xtal_accuracy = 1;

 // Initialize the SoftDevice handler module.
 SOFTDEVICE_HANDLER_INIT(&clock_lf_cfg, NULL);

I redownloaded both SDK 12.3 and SDK 15 to make sure I didn't change anything else, but this problem still happens.