Reconnecting issue

Question

Every time I try to connect to Android phone (running Android 7) or nrfConnect, it connects the first time. After I restart the nrf52 DK, the host takes a while to reconnect or does not connect at all, although its previously bonded. Restarting the board helps every time. What could be the issue in my firmware? 
 I tried changing the below parameters - 
 #define MIN_CONN_INTERVAL MSEC_TO_UNITS(7.5/*100*/, UNIT_1_25_MS) /**< Minimum acceptable connection interval (0.1 seconds). */
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(30/*200*/, UNIT_1_25_MS) /**< Maximum acceptable connection interval (0.2 second). */
#define SLAVE_LATENCY 0 /**< Slave latency. */
#define CONN_SUP_TIMEOUT MSEC_TO_UNITS(100/*4000*/, UNIT_10_MS) /**< Connection supervisory timeout (4 seconds). */
 
 I'm using SDK 15.2 with custom gatt & dfu services with uart peripheral. 
 I also tried adding 
 static void whitelist_set(pm_peer_id_list_skip_t skip)
{
 pm_peer_id_t peer_ids[BLE_GAP_WHITELIST_ADDR_MAX_COUNT];
 uint32_t peer_id_count = BLE_GAP_WHITELIST_ADDR_MAX_COUNT;
 ret_code_t err_code = pm_peer_id_list(peer_ids, &peer_id_count, PM_PEER_ID_INVALID, skip);
 APP_ERROR_CHECK(err_code);
 NRF_LOG_INFO("	m_whitelist_peer_cnt %d, MAX_PEERS_WLIST %d", peer_id_count + 1, BLE_GAP_WHITELIST_ADDR_MAX_COUNT);
 //err_code = pm_whitelist_set(peer_ids, peer_id_count);
	err_code = pm_whitelist_set(NULL, 0);
 APP_ERROR_CHECK(err_code);
} 
 static void advertising_start(bool erase_bonds)
{
 if (erase_bonds == true)
 {
 delete_bonds();
 // Advertising is started by PM_EVT_PEERS_DELETE_SUCCEEDED event.
 }
 else
 {
 whitelist_set(PM_PEER_ID_LIST_SKIP_NO_ID_ADDR);
 uint32_t err_code = ble_advertising_start(&m_advertising, BLE_ADV_MODE_FAST);
 APP_ERROR_CHECK(err_code);
 NRF_LOG_DEBUG("advertising is started");
 }
} 
 case PM_EVT_CONN_SEC_CONFIG_REQ:
 {
 // Reject pairing request from an already bonded peer.
 pm_conn_sec_config_t conn_sec_config = {.allow_repairing = true};
 pm_conn_sec_config_reply(p_evt->conn_handle, &conn_sec_config);
 } break; 
 My advertising_init() - 
 static void advertising_init(void)
{
 uint32_t err_code;
 ble_advertising_init_t init;
 memset(&init, 0, sizeof(init));
 init.advdata.name_type = BLE_ADVDATA_FULL_NAME;
 init.advdata.include_appearance = true;
 init.advdata.flags = BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE;
 //init.advdata.uuids_complete.uuid_cnt = 1;//sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
 //init.advdata.uuids_complete.p_uuids = m_adv_uuids;
	//init.advdata.uuids_complete.p_uuids = &m_adv_uuids[1];
	/*new*/
	init.config.ble_adv_whitelist_enabled = false;//true;	/*BEBOP*/
	init.srdata.name_type = BLE_ADVDATA_NO_NAME;//BLE_ADVDATA_NO_NAME;
	init.srdata.uuids_complete.uuid_cnt = 1;//sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
	init.srdata.uuids_complete.p_uuids = &m_adv_uuids[0];
	init.srdata.uuids_more_available.uuid_cnt = 1;
	init.srdata.uuids_more_available.p_uuids = &m_adv_uuids[1];
	/*new*/
	init.config.ble_adv_fast_enabled = true;
 init.config.ble_adv_fast_interval = APP_ADV_INTERVAL;
 init.config.ble_adv_fast_timeout = APP_ADV_DURATION;
	init.config.ble_adv_extended_enabled = true;
	
 advertising_config_get(&init.config);
 init.evt_handler = on_adv_evt;
 err_code = ble_advertising_init(&m_advertising, &init);
 APP_ERROR_CHECK(err_code);
 ble_advertising_conn_cfg_tag_set(&m_advertising, APP_BLE_CONN_CFG_TAG);
}