_pickle.UnpicklingError: unpickling stack underflow in server.py

[gmolledaj]

$ python3 ./server.py
pygame 2.1.2 (SDL 2.0.16, Python 3.8.10)
Hello from the pygame community. https://www.pygame.org/contribute.html
[SERVER] Started!
New client connected from ('127.0.0.1', 50086)
[CLIENT 7ba0b862c39c4c1e82c47bdc45d659fb] Registered!
Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
self.run()
File "/usr/lib/python3.8/threading.py", line 870, in run
self._target(*self._args, **self._kwargs)
File "./server.py", line 47, in listen
decoded = pickle.loads(incoming_msg)
_pickle.UnpicklingError: unpickling stack underflow