BLE_GAP_EVT_DISCONNECTED Reason 0x2A

Hi,I need your help.

I use NRF51822QFAA, SDK nRF51_SDK_9.0.0 and iPhone 11 ( IOS 13.2) 

I use a project is ble_app_ancs_c at nRF51_SDK_9.0.0\examples\ble_peripheral\ble_app_ancs_c\pca10028\s110\arm4

I modified the following content:

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(500, UNIT_1_25_MS) /**< Minimum acceptable connection interval (0.5 seconds). */
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(1000, UNIT_1_25_MS) /**< Maximum acceptable connection interval (1 second). */
#define SLAVE_LATENCY 0 /**< Slave latency. */
#define CONN_SUP_TIMEOUT MSEC_TO_UNITS(4000, UNIT_10_MS) /**< Connection supervisory time-out (4 seconds). */

after modified:

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(220, UNIT_1_25_MS) /**< Minimum acceptable connection interval (0.5 seconds). */
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(280, UNIT_1_25_MS) /**< Maximum acceptable connection interval (1 second). */
#define SLAVE_LATENCY 4 /**< Slave latency. */
#define CONN_SUP_TIMEOUT MSEC_TO_UNITS(6000, UNIT_10_MS) /**< Connection supervisory time-out (4 seconds). */

The problem is that the connection to the phone is often broken, the reason is 0x2A