Device connects then disconnects immediately

[apdobaj]

This behavior only occurs when connecting to the phone using the native connection procedure, it does not disconnect when using the nRF Connect app on the phone (Android Pixel 3a). Wireshark and the packet sniffer didn't shed much light, I've played with the connection interval settings, slave latency, update count etc. when I play with the max connection interval and the MTU settings I get a hardware fault.

[apdobaj]

I can cause the connection to drop within nRF Connect just by reading the characteristics.

[Hung Bui]

Please capture and send us a sniffer trace. 

Also please check the disconnect reason when you receive the BLE_GAP_EVT_DISCONNECTED event

[apdobaj]

the code never reaches that case in the ble_evt_handler

static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context)
{
    ret_code_t err_code;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GAP_EVT_CONNECTED:
            NRF_LOG_INFO("Connected");
            err_code = bsp_indication_set(BSP_INDICATE_CONNECTED);
            APP_ERROR_CHECK(err_code);
            m_conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
            err_code = nrf_ble_qwr_conn_handle_assign(&m_qwr, m_conn_handle);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GAP_EVT_DISCONNECTED:
            NRF_LOG_INFO("Disconnected");
            
            // Dequeue all keys without transmission.
            (void) buffer_dequeue(false);

            m_conn_handle = BLE_CONN_HANDLE_INVALID;

[Hung Bui]

There must be something wrong that crashed the code make it not reached the BLE_GAP_EVT_DISCONNECTED. 
Please follow this debugging tip: https://devzone.nordicsemi.com/question/60125/my-device-is-freezing-and-restarting/#60126

And please capture a sniffer trace. 

[apdobaj]

Defining DEBUG in the preprocessor doesn't do anything, are there other flags I need to set? Here is the sniffer trace, device is "gestr2"

Wireshark_gestr2.txt