Plotly Dash, No module named 'dash_extensions.websockets'

I have a problem with running my Dash application.

Error:

from dash_extensions.websockets import run_server
ModuleNotFoundError: No module named 'dash_extensions.websockets'

Additional info:

• six months earlier such a problem wasn’t presented (last code modification was 30 March and all worked!)
• but now after some pause I tried to run the application and got error about dash_extensions (no code modifications are made, but linux distro is changed from LinuxMint to UbuntuCinnamon, and thus miniconda freshely installed)

I am using conda. The package dash_extensions is installed and presented in the site-packages folder, but error is raised.

For information, I have package requirements described in the file:

name: vital_dash
channels:
  - conda-forge
  - defaults
dependencies:
  - conda-build
  - python
  - pandas
  - autopep8
  - icecream
  - flask-socketio
  - gevent
  - gevent-websocket
  - websocket-client
  - dash
  - dash-core-components
  - dash-html-components
  - dash-bootstrap-components
  - dash-daq
  - pip
  - pip:
    - Flask-Sockets
    - dash-extensions
    - circular-buffer-numpy

I have tried change python version, which I used earlier, but no positive results.