Reading Mavlink packets from pymavlink (only heartbeat)

We are trying to make our own gui for a competition. When we connect pixhawk via USB port and try to get telemetry values with pymavlink, the pixhawk only sends heartbeat messages and the occasional TIMESYNC message. We are using the exact same code as the one on the ardusub documentation. We can display the values on QGroundControl but pymavlink only receives the heartbeat messages for some reason. After opening and closing QGC, we get correct packets for a few seconds but after rerunning the code a few seconds later we again receive only heartbeat messages. We also tried to send heartbeat with this code:

Example of how to connect pymavlink to an autopilot via an UDP connection

# Disable "Bare exception" warning
# pylint: disable=W0702

import time
# Import mavutil
from pymavlink import mavutil
import threading
mavlink = mavutil.mavlink

class WriteLockedFile(object):
    # A file with thread-locked writing. 
    def __init__(self, file):
        self._base_file = file
        self._write_lock = threading.Lock()
    def write(self, *args, **kwargs):
        with self._write_lock:
            self._base_file.write(*args, **kwargs)
    def __getattr__(self, name):
        return getattr(self._base_file, name)
    def __dir__(self):
        return dir(self._base_file) + ["_base_file", "_write_lock"]

class mavactive(object):
    """ A class for managing an active mavlink connection. """
    def __init__(self, connection, type_=mavlink.MAV_TYPE_GENERIC, autopilot=mavlink.MAV_AUTOPILOT_INVALID, base_mode=0, custom_mode=0,
                 mavlink_version=0, heartbeat_period=0.95):
        """ Initialises the program state and starts the heartbeat thread. """
        self.connection = connection
        self.type = type_
        self.autopilot = autopilot
        self.base_mode = base_mode
        self.custom_mode = custom_mode
        self.mavlink_version = mavlink_version
        self.heartbeat_period = heartbeat_period
        # replace internal file with a thread-safe one
        self.connection.mav.file = WriteLockedFile(self.connection.mav.file)
        # set up the kill event and initialise the heartbeat thread
        self._kill = threading.Event()

    def _birth(self):
        """ Creates and starts the heartbeat thread. """
        self.heartbeat_thread = threading.Thread(target=self.heartbeat_repeat)

    def is_alive(self):
        return not self._kill.is_set()

    def heartbeat_repeat(self):
        """ Sends a heartbeat to 'self.connection' with 'self.heartbeat_period'. """
        while self.is_alive:

    def kill(self):
        """ Stops the heartbeat, if not already dead. """
        if not self.is_alive:
            return # already dead

        del self.heartbeat_thread

    def revive(self):
        """ Starts the heartbeat, if not already alive. """
        if self.is_alive:
            return # already alive


    def __del__(self):
        """ End the thread cleanly on program end. """
# Create the connection
#  If using a companion computer
#  the default connection is available
#  at ip and the port 14550
# Note: The connection is done with 'udpin' and not 'udpout'.
#  You can check in http: that the communication made for 14550
#  uses a 'udpbcast' (client) and not 'udpin' (server).
#  If you want to use QGroundControl in parallel with your python script,
#  it's possible to add a new output port in http: as a new line.
#  E.g: --out udpbcast:
master = mavutil.mavlink_connection("/dev/ttyACM0", baud=115200)

# Make sure the connection is valid

heartbeatPulser = mavactive(master)
# Get some information !
while True:
        rcvpacket = master.recv_match().to_dict()
        if rcvpacket["mavpackettype"] == "AHRS2":
            print("AHRS2 Value")

# Output:
# {'mavpackettype': 'AHRS2', 'roll': -0.11364290863275528, 'pitch': -0.02841472253203392, 'yaw': 2.0993032455444336, 'altitude': 0.0, 'lat': 0, 'lng': 0}
# {'mavpackettype': 'AHRS3', 'roll': 0.025831475853919983, 'pitch': 0.006112074479460716, 'yaw': 2.1514968872070312, 'altitude': 0.0, 'lat': 0, 'lng': 0, 'v1': 0.0, 'v2': 0.0, 'v3': 0.0, 'v4': 0.0}
# {'mavpackettype': 'VFR_HUD', 'airspeed': 0.0, 'groundspeed': 0.0, 'heading': 123, 'throttle': 0, 'alt': 3.129999876022339, 'climb': 3.2699999809265137}
# {'mavpackettype': 'AHRS', 'omegaIx': 0.0014122836291790009, 'omegaIy': -0.022567369043827057, 'omegaIz': 0.02394154854118824, 'accel_weight': 0.0, 'renorm_val': 0.0, 'error_rp': 0.08894175291061401, 'error_yaw': 0.0990816056728363}

Hi @Efe,

Please see this post: