AwsCrtError: AWS_ERROR_MQTT_UNEXPECTED_HANGUP

I clone this repo on my jetson nano board, and successfully install dependencies.
I checked openssl connection to my iot endpoint, and it also success.
But when I run `python3 main.py` I get this error
```
Traceback (most recent call last):
File "main.py", line 81, in
run_provisioning(isRotation=False)
File "main.py", line 74, in run_provisioning
provisioner.get_official_certs(callback)
File "/home/li/IOT/aws-iot-fleet-provisioning/provisioning_handler.py", line 161, in get_official_certs
return asyncio.run(self.orchestrate_provisioning_flow(callback))
File "/usr/lib/python3.7/asyncio/runners.py", line 43, in run
return loop.run_until_complete(main)
File "/usr/lib/python3.7/asyncio/base_events.py", line 587, in run_until_complete
return future.result()
File "/home/li/IOT/aws-iot-fleet-provisioning/provisioning_handler.py", line 165, in orchestrate_provisioning_flow
self.core_connect()
File "/home/li/IOT/aws-iot-fleet-provisioning/provisioning_handler.py", line 102, in core_connect
connect_future.result()
File "/usr/lib/python3.7/concurrent/futures/_base.py", line 435, in result
return self.__get_result()
File "/usr/lib/python3.7/concurrent/futures/_base.py", line 384, in __get_result
raise self._exception
awscrt.exceptions.AwsCrtError: AwsCrtError(name='AWS_ERROR_MQTT_UNEXPECTED_HANGUP', message='The connection was closed unexpectedly.', code=5134)
```
I checked policy as well, and it looks correct.