nrf9160 modem blocking issue

CMakeLists.txt

cmake_minimum_required(VERSION 3.13.1)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(nrf91-block)

target_sources(app PRIVATE src/main.c)

main.c

#include <zephyr.h>                                                                                                                                           
#include <string.h>                                                                                                                                           
#include <modem/modem_key_mgmt.h>                                                                                                                             
#include <net/mqtt.h>                                                                                                                                         
                                                                                                                                                              
#include <net/ethernet.h>                                                                                                                                     
static int eth_dummy_init(struct device *dev)                                                                                                                 
{                                                                                                                                                             
        return 0;                                                                                                                                             
}                                                                                                                                                             
                                                                                                                                                              
ETH_NET_DEVICE_INIT(eth_dummy, "eth_dummy", eth_dummy_init, NULL, NULL, NULL, CONFIG_ETH_INIT_PRIORITY, NULL, NET_ETH_MTU);

/* Amazon AWS rootCA */
#define CA_CERTIFICATE \
"-----BEGIN CERTIFICATE-----\n" \
"MIIDQTCCAimgAwIBAgITBmyfz5m/jAo54vB4ikPmljZbyjANBgkqhkiG9w0BAQsF\n" \
"ADA5MQswCQYDVQQGEwJVUzEPMA0GA1UEChMGQW1hem9uMRkwFwYDVQQDExBBbWF6\n" \
"b24gUm9vdCBDQSAxMB4XDTE1MDUyNjAwMDAwMFoXDTM4MDExNzAwMDAwMFowOTEL\n" \
"MAkGA1UEBhMCVVMxDzANBgNVBAoTBkFtYXpvbjEZMBcGA1UEAxMQQW1hem9uIFJv\n" \
"b3QgQ0EgMTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALJ4gHHKeNXj\n" \
"ca9HgFB0fW7Y14h29Jlo91ghYPl0hAEvrAIthtOgQ3pOsqTQNroBvo3bSMgHFzZM\n" \
"9O6II8c+6zf1tRn4SWiw3te5djgdYZ6k/oI2peVKVuRF4fn9tBb6dNqcmzU5L/qw\n" \
"IFAGbHrQgLKm+a/sRxmPUDgH3KKHOVj4utWp+UhnMJbulHheb4mjUcAwhmahRWa6\n" \
"VOujw5H5SNz/0egwLX0tdHA114gk957EWW67c4cX8jJGKLhD+rcdqsq08p8kDi1L\n" \
"93FcXmn/6pUCyziKrlA4b9v7LWIbxcceVOF34GfID5yHI9Y/QCB/IIDEgEw+OyQm\n" \
"jgSubJrIqg0CAwEAAaNCMEAwDwYDVR0TAQH/BAUwAwEB/zAOBgNVHQ8BAf8EBAMC\n" \
"AYYwHQYDVR0OBBYEFIQYzIU07LwMlJQuCFmcx7IQTgoIMA0GCSqGSIb3DQEBCwUA\n" \
"A4IBAQCY8jdaQZChGsV2USggNiMOruYou6r4lK5IpDB/G/wkjUu0yKGX9rbxenDI\n" \
"U5PMCCjjmCXPI6T53iHTfIUJrU6adTrCC2qJeHZERxhlbI1Bjjt/msv0tadQ1wUs\n" \
"N+gDS63pYaACbvXy8MWy7Vu33PqUXHeeE6V/Uq2V8viTO96LXFvKWlJbYK8U90vv\n" \
"o/ufQJVtMVT8QtPHRh8jrdkPSHCa2XV4cdFyQzR1bldZwgJcJmApzyMZFo6IQ6XU\n" \
"5MsI+yMRQ+hDKXJioaldXgjUkK642M4UwtBV8ob2xJNDd2ZhwLnoQdeXeGADbkpy\n" \
"rqXRfboQnoZsG4q5WTP468SQvvG5\n" \
"-----END CERTIFICATE-----\n"

#define CONFIG_MQTT_TLS_SEC_TAG         24
void main(void)
{
        int err;

        err = modem_key_mgmt_write(CONFIG_MQTT_TLS_SEC_TAG,
                                   MODEM_KEY_MGMT_CRED_TYPE_CA_CHAIN,
                                   CA_CERTIFICATE,
                                   strlen(CA_CERTIFICATE));
        if (err) {
                printk("Failed to provision CA certificate, err %d\n", err);
                return;
        }

        printk("Key write successfull\n");
}

prj.conf

CONFIG_NETWORKING=y
CONFIG_NET_NATIVE=y
CONFIG_NET_SOCKETS_OFFLOAD=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_POSIX_NAMES=y
CONFIG_LTE_LINK_CONTROL=y
CONFIG_BSD_LIBRARY=y
CONFIG_MODEM_KEY_MGMT=y
CONFIG_HEAP_MEM_POOL_SIZE=2048
CONFIG_NET_L2_ETHERNET=y
CONFIG_NET_CONNECTION_MANAGER=y