Python request module sometimes throws WinError 10049

I'm using docker-compose to run a fastapi-app, an Nginx server and an certbot container. But sometimes when i try to reach the Nginx server via port 80/443 with the python request-module, I get HTTPSConnectionPool(host='<gamagu.dynv6.net>', port=443): Max retries exceeded with url: /token (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x00000203CD66C310>: Failed to establish a new connection: [WinError 10049] Die angeforderte Adresse ist in diesem Kontext ungültig')) Most of the time, via Firefox is the server still reachable.