Yeah, that was my idea as well. Especially since I got UDP to work in all directions.
Unfortunately changing the port, changes nothing in the results:
I have tested the server by also creating a Python3 client, that sends a message to the same Python3 server I try to use with the STM32 client. That Python3 client does work on port 80 (and port 10001 for that matter):
I really don’t see what I could’ve done different 
Thanks in advance.