A strange problem about download and debug

Hello, I made some boards on nrf52832 and I was testing the PCB.

The test program is ..\nRF5_SDK_12.0.0_12f24da\examples\ble_peripheral\ble_app_hrs.

(I have downloaded the softdevice s132 3.0.0)

Here the appearance as follows:

  • In debug mode:

image description and run, everything is fine.

  • In download mode:

image description image description

can scan the advertise, but can't connect.

So I add uart to print some error message in download mode. And I find it will run into app_error_fault.

void app_error_fault_handler(uint32_t id, uint32_t pc, uint32_t info)
    error_info_t* error_info = (error_info_t*)info;
    memset(error_buffer, 0x00, sizeof(error_buffer));
            "app_error file_name: %s, line_num: %d, err_code: %08X\r\n",
            error_info->p_file_name, error_info->line_num, error_info->err_code

And the uart print message is :

app_error file_name: KGJ`h侒園h, line_num: 1024, err_code: 00000579

But I can't find any error code about 579. What is the reason?

Is the chip wrong or my board design? Or else?

I need you help!