"Dictionary size changed during iteration" error

I left the server running for a while, and came back to this error:

/tmp/accesspluspython/./access.py:6883: DeprecationWarning: isSet() is deprecated, use is_set() instead
  if event.isSet(): return
Started sharing
/tmp/accesspluspython/./access.py:1377: DeprecationWarning: isSet() is deprecated, use is_set() instead
  if not evt.isSet():
/tmp/accesspluspython/./access.py:1381: DeprecationWarning: isSet() is deprecated, use is_set() instead
  return evt.isSet()
/tmp/accesspluspython/./access.py:4970: DeprecationWarning: isSet() is deprecated, use is_set() instead
  if event.isSet(): return
/tmp/accesspluspython/./access.py:2392: DeprecationWarning: isSet() is deprecated, use is_set() instead
  if self.event.isSet():
Exception in thread Listener:
Traceback (most recent call last):
  File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.12/threading.py", line 1010, in run
    self._target(*self._args, **self._kwargs)
  File "/tmp/accesspluspython/./access.py", line 6841, in listen
    self.read_poll_socket()
  File "/tmp/accesspluspython/./access.py", line 5383, in read_poll_socket
    self._read_poll_socket(data, address)
  File "/tmp/accesspluspython/./access.py", line 5770, in _read_poll_socket
    self.cleanup_handles(host)
  File "/tmp/accesspluspython/./access.py", line 4586, in cleanup_handles
    share.cleanup_handles(host)
  File "/tmp/accesspluspython/./access.py", line 2287, in cleanup_handles
    for handle in self.file_handler.keys():
RuntimeError: dictionary changed size during iteration