Dear @minrk and all, I've been pulling my hair for these past few days trying to understand what's wrong with my codes and how to fix it, so I hope you can help me!

Just so can you understand my "journey": I'm using ipyparallel together with bluepyopt to do a morphospace exploration, and the script calls for matlab to run a function with given values that fluctuate between a range. When I run my code with parallelization (which I do manually with ipcontroller and ipengine), all engines can finish except one, which stays "frozen" in matlab for hours (longest time I have left it running was around 8h, while all other engines finish in less than 1h). However, if I run the codes by calling the matlab function everytime with the same values, all engines complete in less than 1h, and in the end of the code I have a shutdown request by the client that gives an error. So I decided to go back to basics and see if this was an overall problem with ipyparallel.
I just did a script that starts a controller with one engine, starts a client, prints the id, and then does a shutdown request.
The code is as follow:

import os
import ipyparallel as ipp
from time import sleep
os.system('''START "controller" ipcontroller --log-to-file &''')
sleep(15)
tc = ipp.Client()
os.system('''START "engine 0" ipengine &''')
sleep(30)
tc = ipp.Client()
print(tc)
print(tc.ids)
sleep(10)
tc.shutdown(hub = True)

The console output:

<ipyparallel.client.client.Client object at 0x000001CE4D8714E0>
[0]

The controller window, right before shuting down, shows:

Unhandled message type: 'shutdown_notification'
ERROR:scheduler:Unhandled message type: 'shutdown_notification'

The error I see in logfile of the controller:

ERROR | Uncaught exception in <function Hub.dispatch_monitor_traffic at 0x000001F9A099C6A8>
Traceback (most recent call last):
File "C:\Users\Natii\Anaconda3\lib\site-packages\ipyparallel\util.py", line 119, in log_errors
return f(self, *args, **kwargs)
File "C:\Users\Natii\Anaconda3\lib\site-packages\ipyparallel\controller\hub.py", line 520, in dispatch_monitor_traffic
handler(idents, msg)
File "C:\Users\Natii\Anaconda3\lib\site-packages\ipyparallel\controller\hub.py", line 846, in monitor_iopub_message
uuid = self.engines[eid].uuid
KeyError: None
client::client b'\x00\x80\x00\x00-' requested 'shutdown_request'
hub::hub shutting down.

I also sometimes (yes, only sometimes, don't ask me why...) get this output on the console:
(in the first exception, the value of the handle, 2204, changes every time, and in the second exception, the number of the thread, Thread-16, also changes)

Exception in callback BaseAsyncIOLoop._handle_events(2204, 1)
handle: <Handle BaseAsyncIOLoop._handle_events(2204, 1)>
Traceback (most recent call last):
File "C:\Users\Natii\Anaconda3\lib\asyncio\events.py", line 88, in _run
self._context.run(self._callback, *self._args)
File "C:\Users\Natii\Anaconda3\lib\site-packages\tornado\platform\asyncio.py", line 122, in _handle_events
handler_func(fileobj, events)
File "C:\Users\Natii\Anaconda3\lib\site-packages\tornado\stack_context.py", line 300, in null_wrapper
return fn(*args, **kwargs)
File "C:\Users\Natii\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 465, in _handle_events
self._rebuild_io_state()
File "C:\Users\Natii\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 522, in _rebuild_io_state
self._update_handler(state)
File "C:\Users\Natii\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 539, in _update_handler
if state & self.socket.events:
File "C:\Users\Natii\Anaconda3\lib\site-packages\zmq\sugar\attrsettr.py", line 48, in __getattr__
return self._get_attr_opt(upper_key, opt)
File "C:\Users\Natii\Anaconda3\lib\site-packages\zmq\sugar\attrsettr.py", line 52, in _get_attr_opt
return self.get(opt)
File "zmq\backend\cython\socket.pyx", line 477, in zmq.backend.cython.socket.Socket.get
File "zmq\backend\cython\socket.pyx", line 135, in zmq.backend.cython.socket._check_closed
zmq.error.ZMQError: Unknown error
Exception in thread Thread-16:
Traceback (most recent call last):
File "C:\Users\Natii\Anaconda3\lib\threading.py", line 917, in _bootstrap_inner
self.run()
File "C:\Users\Natii\Anaconda3\lib\threading.py", line 865, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\Natii\Anaconda3\lib\site-packages\ipyparallel\client\client.py", line 901, in _io_main
self._io_loop.start()
File "C:\Users\Natii\Anaconda3\lib\site-packages\tornado\platform\asyncio.py", line 132, in start
self.asyncio_loop.run_forever()
File "C:\Users\Natii\Anaconda3\lib\asyncio\base_events.py", line 528, in run_forever
self._run_once()
File "C:\Users\Natii\Anaconda3\lib\asyncio\base_events.py", line 1728, in _run_once
event_list = self._selector.select(timeout)
File "C:\Users\Natii\Anaconda3\lib\selectors.py", line 323, in select
r, w, _ = self._select(self._readers, self._writers, [], timeout)
File "C:\Users\Natii\Anaconda3\lib\selectors.py", line 314, in _select
r, w, x = select.select(r, w, w, timeout)
OSError: [WinError 10038] An operation was attempted on something that is not a socket

So long story short, there is some error associated with the client().shutdown(), that happens both for hub = True or hub = False. The error in the console, happens only when hub = True. I don't know if this is why my original code is not finishing...

I am using Windows 10 64-bit, pyhton version 3.7.1.final.0 on conda version 4.6.12.
I would really appreciate any help you could give me!!!