flask socketio backgroundtask stops after http post

Question

Anytime I sent a post request to /tts/say or any other post request, the background task stops. Why is that and most importantly, how can I stop this behavior? I wasn't able to find more useful information, so if you miss some information, just ask, and I will try to provide it as quickly as possible. In the pepper.py there is connection to a python2 script via the socket module over port 9999. Here's the code from the main app.py:

    import os
    from flask import Flask
    import flask
    from flask_socketio import SocketIO
    
    
    import pepper
    import config
    
    app = Flask(__name__)
    socketio = SocketIO(app)
    
    pepper = pepper.Pepper()
    
    
    @app.route('/')
    def main_get():  # put application's code here
        return flask.render_template(
            'index.html',
            autonomous_life_options=pepper.get_autonomous_life_options(),
            apps=pepper.get_installed_apps(),
            postures=pepper.get_postures()
        )
    
    @app.route('/tts/say', methods=['POST'])
    def tts_say():
        text = flask.request.get_json()['text']
        pepper.say(text)
        return flask.Response("OK", status=200)
    
    ...
    
    @socketio.on('connect')
    def handle_connect():
        print('Client connected: ', flask.request.remote_addr)
    
    def send_updates():
        while True:
            socketio.sleep(1)
            print("sending...")
            socketio.emit('update_values', {
                'volume': pepper.get_volume(),
                'tablet_brightness': pepper.get_tablet_brightness(),
                'autonomous_life_state': pepper.get_autonomous_life(),
                'battery_level': pepper.get_battery_level(),
                'apps_is_running': pepper.apps_is_running
            })
    
    
    if __name__ == '__main__':
        socketio.start_background_task(send_updates)
        socketio.run(app, **config.server_config_args)
        print("Server listening on port 5005")

Edit:

I now suspect the socket connection out of pepper.py (import socket) as if I modify my code to be more like this example (https://github.com/miguelgrinberg/Flask-SocketIO/blob/main/example/app.py) it still doesn't work, but if I run it without the pepper.py (in a test file) it works. I think I got near to what causes the problem, but I still don't understand why and who to fix it.