Precise data bus error on mqtt_helper_thread

Question

Hi,

I have an application that each 30 minutes connects to AWS, sends some data and then disconnects and goes to sleep. I have based my aplication on the asset_tracker application example.

The first time the devices connects to the AWS cloud everything works correctly. The device connects to AWS, sends the data and disconnects. But the second time it tries to connect I get the following error:

```

[00:00:49.673,004] <inf> app_event_manager: DATA_EVT_DATA_READY
[00:00:49.679,687] <inf> cloud_module: Connecting to AWS IoT Core
[00:00:49.686,309] <dbg> aws_iot: aws_iot_connect: No hostname provided, using Kconfig value: ---------ats.iot.us-east-1.amazonaws.com
[00:00:53.357,116] <dbg> aws_iot: on_connack: MQTT client connected!
[00:00:53.366,302] <err> os: ***** BUS FAULT *****
[00:00:53.371,765] <err> os: Precise data bus error
[00:00:53.377,502] <err> os: BFAR Address: 0x0
[00:00:53.382,873] <err> os: r0/a1: 0x73776124 r1/a2: 0x00067f62 r2/a3: 0x00000000
[00:00:53.391,601] <err> os: r3/a4: 0x73776124 r12/ip: 0x00000000 r14/lr: 0x0001cbeb
[00:00:53.400,299] <err> os: xpsr: 0x61000000
[00:00:53.405,578] <err> os: s[ 0]: 0x200156f0 s[ 1]: 0x20015664 s[ 2]: 0x00000001 s[ 3]: 0x00000 000
[00:00:53.416,046] <err> os: s[ 4]: 0x00000000 s[ 5]: 0x0003d855 s[ 6]: 0x00000000 s[ 7]: 0x0003d 925
[00:00:53.426,544] <err> os: s[ 8]: 0x00000010 s[ 9]: 0x00000000 s[10]: 0x20015664 s[11]: 0x0003c 253
[00:00:53.437,011] <err> os: s[12]: 0x00050cd5 s[13]: 0x00040109 s[14]: 0x00000000 s[15]: 0x00000 000
[00:00:53.447,479] <err> os: fpscr: 0x00000000
[00:00:53.452,728] <err> os: Faulting instruction address (r15/pc): 0x00009038
[00:00:53.460,662] <err> os: >>> ZEPHYR FATAL ERROR 25: Unknown error on CPU 0
[00:00:53.468,627] <err> os: Current thread: 0x20012c98 (mqtt_helper_thread)

```

This is my prj.conf

```

# General

CONFIG_PICOLIBC=y

CONFIG_FPU=y

CONFIG_STDOUT_CONSOLE=y

CONFIG_LOG=y

CONFIG_LOG_MODE_IMMEDIATE=y

CONFIG_ASSERT=y

CONFIG_INIT_STACKS=y

# We are simulating transmission of frames 0 NO, 1 YES

CONFIG_IS_SIMULATION=0

#logging

CONFIG_LOG_MAX_LEVEL=4

CONFIG_MODEM_MODULE_LOG_LEVEL_DBG=y

CONFIG_APP_MODULE_LOG_LEVEL_DBG=y

CONFIG_DATA_MODULE_LOG_LEVEL_DBG=y

CONFIG_CLOUD_MODULE_LOG_LEVEL_DBG=y

CONFIG_CONFIG_MODULE_LOG_LEVEL_DBG=y

CONFIG_SENSOR_MODULE_LOG_LEVEL_DBG=y

CONFIG_LOCATION_MODULE_LOG_LEVEL_DBG=y

CONFIG_CLOUD_CODEC_LOG_LEVEL_DBG=y

CONFIG_BUTTONS_MODULE_LOG_LEVEL_DBG=y

CONFIG_LEDS_MODULE_LOG_LEVEL_DBG=y

CONFIG_EXT_MEMORY_MODULE_LOG_LEVEL_DBG=y

CONFIG_FLASH_LOG_LEVEL_DBG=y

# nRF modem library

CONFIG_NRF_MODEM_LIB=y

CONFIG_NRF_MODEM_LIB_ON_FAULT_APPLICATION_SPECIFIC=y

# NEWLIB C

CONFIG_NEWLIB_LIBC=y

CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y

CONFIG_NEWLIB_LIBC_FLOAT_SCANF=y

CONFIG_TIMING_FUNCTIONS=y

CONFIG_CBPRINTF_FP_SUPPORT=y

# Memory and stack configuration

CONFIG_HEAP_MEM_POOL_SIZE=15200

CONFIG_MAIN_STACK_SIZE=8190

CONFIG_AT_MONITOR_HEAP_SIZE=1024

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=4096

CONFIG_HW_STACK_PROTECTION=y

CONFIG_THREAD_NAME=y

# CJSON

CONFIG_CJSON_LIB=y

# Configuration required by Event Manager

CONFIG_APP_EVENT_MANAGER=y

CONFIG_APP_EVENT_MANAGER_LOG_EVENT_TYPE=n

# CAF - Common Application Framework

CONFIG_CAF=y

# LTE Link Control

CONFIG_LTE_LINK_CONTROL=y

CONFIG_LTE_NETWORK_MODE_LTE_M_GPS=y

# CONFIG_LTE_MODE_PREFERENCE_LTE_M_PLMN_PRIO=y

CONFIG_LTE_MODE_PREFERENCE_LTE_M=y

CONFIG_LTE_LINK_CONTROL_LOG_LEVEL_DBG=y

# CONFIG_LTE_LINK_CONTROL_LOG_LEVEL_CHOICE=CONFIG_LTE_LINK_CONTROL_LOG_LEVEL_DBG

# Networking

CONFIG_NETWORKING=y

CONFIG_NET_SOCKETS=y

CONFIG_NET_SOCKETS_OFFLOAD=y

# Date Time library

CONFIG_DATE_TIME=y

CONFIG_DATE_TIME_AUTO_UPDATE=y

# AWS IoT library

CONFIG_AWS_IOT=y

CONFIG_AWS_IOT_BROKER_HOST_NAME="--------------ats.iot.us-east-1.amazonaws.com"

CONFIG_MQTT_HELPER_SEC_TAG=16842753

CONFIG_AWS_IOT_TOPIC_UPDATE_DELTA_SUBSCRIBE=y

CONFIG_AWS_IOT_AUTO_DEVICE_SHADOW_REQUEST=n

CONFIG_AWS_IOT_TOPIC_UPDATE_ACCEPTED_SUBSCRIBE=n

CONFIG_AWS_IOT_TOPIC_DELETE_ACCEPTED_SUBSCRIBE=n

CONFIG_AWS_IOT_TOPIC_DELETE_REJECTED_SUBSCRIBE=n

CONFIG_AWS_IOT_TOPIC_GET_REJECTED_SUBSCRIBE=n

CONFIG_AWS_IOT_TOPIC_GET_ACCEPTED_SUBSCRIBE=n

CONFIG_MQTT_CLEAN_SESSION=y

CONFIG_AWS_IOT_LOG_LEVEL_DBG=y

# Power manager

CONFIG_PM_DEVICE=y

CONFIG_PM=y

# FOTA Download

CONFIG_AWS_FOTA=y

CONFIG_FOTA_DOWNLOAD=y

CONFIG_DOWNLOAD_CLIENT=y

CONFIG_DOWNLOAD_CLIENT_STACK_SIZE=4096

# DFU Target

CONFIG_DFU_TARGET=y

CONFIG_DFU_TARGET_STREAM_SAVE_PROGRESS=y

# Settings

CONFIG_SETTINGS=y

CONFIG_SETTINGS_NVS=y

# Non-volatile Storage

CONFIG_NVS=y

# # Application update support

# # CONFIG_BOOTLOADER_MCUBOOT=y

# Image manager

CONFIG_IMG_MANAGER=y

CONFIG_FLASH=y

CONFIG_IMG_ERASE_PROGRESSIVELY=y

CONFIG_FLASH_MAP=y

CONFIG_FLASH_PAGE_LAYOUT=y

# # CONFIG_PM_EXTERNAL_FLASH_MCUBOOT_SECONDARY=n

# FILE SYSTEM

CONFIG_FLASH_JESD216_API=y

CONFIG_FILE_SYSTEM=n

CONFIG_MPU_ALLOW_FLASH_WRITE=y

# # SENSORS

CONFIG_SENSOR=y

# BME680 - Temperature and humidity sensor.

CONFIG_BME680=y

# MAX17262 - Maxim battery fuel gauge

CONFIG_MAX17262=y

# CONFIG_BH1749 - RGB Sensor

CONFIG_BH1749=y

CONFIG_BH1749_TRIGGER=y

# PWM

CONFIG_PWM=y

# SPI external flash

CONFIG_SPI=y

CONFIG_SPI_NOR=y

CONFIG_SPI_NOR_FLASH_LAYOUT_PAGE_SIZE=4096

# CONFIG_PM_EXTERNAL_FLASH_BASE=0x0

#UART GSM

CONFIG_UART_ASYNC_API=y

CONFIG_UART_LINE_CTRL=y

CONFIG_RING_BUFFER=y

# CONFIG_REBOOT=y

# # WiFI

CONFIG_WIFI=y

CONFIG_WIFI_NRF700X=y

CONFIG_WIFI_NRF700X_SKIP_LOCAL_ADMIN_MAC=y

# Scan only using offload API

# CONFIG_WPA_SUPP=n

CONFIG_NRF_WIFI_SCAN_MAX_BSS_CNT=4

CONFIG_WIFI_NRF700X_SCAN_TIMEOUT_S=10

CONFIG_NET_L2_ETHERNET=y

# CONFIG_NET_NATIVE=y

# CONFIG_NET_IPV4=y

# CONFIG_NET_DHCPV4=y

# CONFIG_NET_STATISTICS=y

# CONFIG_NET_STATISTICS_WIFI=y

# CONFIG_NET_STATISTICS_USER_API=y

# CONFIG_NET_CONTEXT_SYNC_RECV=y

# # Disable unused networking options

# CONFIG_NET_IPV6=n

# For nRF9160 the default is socket interface

# CONFIG_NET_DEFAULT_IF_ETHERNET=y

# CONFIG_MBEDTLS=n

# CONFIG_NORDIC_SECURITY_BACKEND=n

```

I'm using NCS 2.6.1