Cannot connect to CloudMQTT provider

Home Assistant release with the issue:
0.81.2
Operating environment (Hass.io/Docker/Windows/etc.):
Hass.io RP3
Description of problem:
I cannot connect to CloudMQTT provider. I got [Errno -3] error which is not too talkative error message. What is the problem? Thanks for your help.
Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

  mqtt:
  broker: m20.cloudmqtt.com
  port: portnumber
  username: ha
  password: ha
  client_id: HomeAssistant

Traceback (if applicable):

8:50 PM components/mqtt/__init__.py (ERROR)
Log Details (ERROR)
Sun Nov 04 2018 20:50:40 GMT+0100 (közép-európai téli idő)

Failed to connect due to exception: [Errno -3] Try again

Additional information:
CloudMQTT ACLs:
[

]

try it without the client_id

Thanks, I already tried it. It’s not working. :frowning: