Strange issue with Python socket

Question

I am facing a strange problem using a simple python client/server example. After having established the connection for the first time, if I tried to send the message "get id", I don't get any answer from my server and client side is stuck (I am developping an application to communicate with a measurement system via ethernet instead of RS232 and "get id" is one of the command we use). However if I start by sending "a" or "1" or even "hello world", the server answers and then if I send "get id" it works !

Now if I run the server code and use Putty as client, I can send "get id" as a first message and the server answers without any problem !

I would like to understand what is going on...

Here is the client code

import socket

host = '192.168.0.102'
port = 12800

connection_with_server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

connection_with_server.connect((host, port))
print("Connexion established on port {}".format(port))
msg = '1'

while msg != b'stopall\r':
    msg = input('> ')
    msg = msg+'\r'
    msg = msg.encode('utf-8')
    connection_with_server.send(msg)
    received_message = connection_with_server.recv(1024)
    print('received message: ', received_message.decode())

print('connection closed')

And server code

import socket
import select

def openEthernetConnection(host,port):
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        s.bind((host, port))
        s.listen(1)
        print("Server is now listening on port {}".format(port))
        return(s)
        
if __name__ == '__main__':
    
    protocole = 'ethernet'
    encode_format = 'utf-8'
       
    if protocole == 'ethernet':
        # open ethernet connection
        host = ''
        port = 12800
        mysocket = openEthernetConnection(host,port)
        clients_connected = []        

    while True:
    
        if protocole == 'ethernet':
            # Check for new clients
            new_connections, wlist, xlist = select.select([mysocket],
                [], [], 0.05)
            for connection in new_connections:
                connexion_with_client, infos_connexion = connection.accept()
                # On ajoute le socket connecté à la liste des clients
                clients_connected.append(connexion_with_client)
            # Listen the list of connected clients
            # select return clients who must be read with recv
            # wait 50ms
            # select.select in a try loop if we want to raise an exception if no clients are connected
            clients_to_read = []
            try:
                clients_to_read, wlist, xlist = select.select(clients_connected,
                        [], [], 0.05)
            except select.error: 
                pass
            else:
                command = []
                # Go through the clients list to be read
                for client in clients_to_read:
                    received_command = client.recv(1024)
                    try:
                        received_command = received_command.decode(encode_format)
                        command = received_command.split()
                        print('command: ', command)
                    except UnicodeDecodeError:
                        return_message = 'E010'
                        pass
       
                for client in clients_to_read:
                    return_message = '5/5'
                    client.sendall(return_message.encode(encode_format))

Thanks for your help !