Could not process inbound connection - Publish with rqt_gui

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Hi,

I was working with a python node that acts as a intermediary node for communication between two other nodes. The problem is that, while the communication between nodes is correct (the messages are being published correctly and the nodes communicate just fine), when I try to publish in the intermediary node topic with rqt_gui the following warning is written in the console:

Could not process inbound connection: [/rqt_gui_py_node_3098] is not a publisher of [/chatter]. Topics are [['/rosout', 'rosgraph_msgs/Log']]{'message_definition': 'string data\n', 'callerid': '/test_node_2922_1564747575437', 'tcp_nodelay': '0', 'md5sum': '992ce8a1687cec8c8bd883ec73ca41d1', 'topic': '/chatter', 'type': 'std_msgs/String'}

This does not happen when publishing on the topic with the proper console command: E.g.: rostopic pub -r 10 /chatter std_msgs/String "data: 'Hello world'"

And I am wondering what is this warning and the reason of it.

I will post here the chunk of code for the intermediary node:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String

def spin():

    rospy.init_node('test_node', anonymous=True)

    rospy.Subscriber('chatter', String, callback)

    pub = rospy.Publisher('talker', String, queue_size=10)
    rate = rospy.Rate(10)
    while not rospy.is_shutdown():
        pub.publish(msg)
        rate.sleep()

    rospy.spin()

msg = None

def callback(data):
    msg = data.data

if __name__ == '__main__':
    try:
        spin()
    except rospy.ROSInterruptException:
        pass

Thanks in advance!