Hello there
The problem I encountered was that when getting the slave service, returning to get the service failed.
I used DEBUG to check the p_ble_gattc_evt->gatt_status in the on_primary_srv_discovery_rsp() function and found that it returned #define BLE_GATT_STATUS_ATTERR_ATTRIBUTE_NOT_FOUND 0x010A, but I checked that the slave service did exist.