JupyterLab from conda on Windows doesn't work

I have successfully used JupyterLab on Linux. Now I can’t get it working on Windows 10. Are there any caveats?
I installed JupyterLab from Miniconda version 4.8.2. Further below I’ll include a list of installed packages. When running “jupyter lab”, I can access the user interface in the browser, but there seems to be no connection to the kernel. This is shown in the powershell:

(jl-ext) PS C:\Users\user> jupyter lab
[W 09:28:18.287 LabApp] Widgets are unavailable. Please install widgetsnbextension or ipywidgets 4.0
[W 09:28:18.297 LabApp] JupyterLab server extension not enabled, manually loading…
[I 09:28:18.601 LabApp] JupyterLab extension loaded from C:\Users\user\miniconda3\envs\jl-ext\lib\site-packages\jupyterlab
[I 09:28:18.601 LabApp] JupyterLab application directory is C:\Users\user\miniconda3\envs\jl-ext\share\jupyter\lab
[I 09:28:18.898 LabApp] Serving notebooks from local directory: C:\Users\user
[I 09:28:18.898 LabApp] 0 active kernels
[I 09:28:18.898 LabApp] The Jupyter Notebook is running at: http://localhost:8888/?token=3be840c541e5142ede4bc8742f9dd60fe25f5af46be6525f
[I 09:28:18.898 LabApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 09:28:18.908 LabApp]

Copy/paste this URL into your browser when you connect for the first time,
to login with a token:

[I 09:28:19.225 LabApp] Accepting one-time-token-authenticated connection from ::1
[W 09:28:19.922 LabApp] 404 GET /metrics?1592378899903 (::1) 22.13ms referer=http://localhost:8888/lab
[I 09:28:20.672 LabApp] Build is up to date
[W 09:28:24.970 LabApp] 404 GET /metrics?1592378904954 (::1) 5.00ms referer=http://localhost:8888/lab
[I 09:28:26.659 LabApp] Creating new notebook in /
[I 09:28:27.060 LabApp] Kernel started: fcec61cf-9152-4509-9fee-688766be8904
C:\Users\user\miniconda3\envs\jl-ext\lib\site-packages\notebook\base\zmqhandlers.py:292: RuntimeWarning: coroutine ‘WebSocketHandler.get’ was never awaited
super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
[W 09:28:28.795 LabApp] Replacing stale connection: fcec61cf-9152-4509-9fee-688766be8904:fdc78728-5644-4783-8f36-6c7122bce8c3
[W 09:28:29.998 LabApp] 404 GET /metrics?1592378909984 (::1) 0.00ms referer=http://localhost:8888/lab
[W 09:28:35.030 LabApp] 404 GET /metrics?1592378915015 (::1) 15.63ms referer=http://localhost:8888/lab
[W 09:28:40.060 LabApp] 404 GET /metrics?1592378920046 (::1) 15.63ms referer=http://localhost:8888/lab
[W 09:28:45.090 LabApp] 404 GET /metrics?1592378925076 (::1) 15.59ms referer=http://localhost:8888/lab
[W 09:28:49.342 LabApp] Replacing stale connection: fcec61cf-9152-4509-9fee-688766be8904:0c77e172-3c46-4bf0-afb2-b635a3fad23a
[W 09:28:50.113 LabApp] 404 GET /metrics?1592378930107 (::1) 0.00ms referer=http://localhost:8888/lab

I read elsewhere that tornado>=6.0.0 was causing similar problems. So I installed tonado 5.1.1. Here is the complete list if installed packages:

arrow 0.15.6 py36h9f0ad1d_1 conda-forge
attrs 19.3.0 py_0 conda-forge
backcall 0.2.0 pyh9f0ad1d_0 conda-forge
binaryornot 0.4.4 py_1 conda-forge
bleach 3.1.5 pyh9f0ad1d_0 conda-forge
brotlipy 0.7.0 py36h779f372_1000 conda-forge
ca-certificates 2020.1.1 0
certifi 2020.4.5.2 py36_0
cffi 1.14.0 py36ha419a9e_0 conda-forge
chardet 3.0.4 py36h9f0ad1d_1006 conda-forge
click 7.1.2 pyh9f0ad1d_0 conda-forge
colorama 0.4.3 py_0 conda-forge
cookiecutter 1.7.2 pyh9f0ad1d_0 conda-forge
cryptography 2.9.2 py36hef61171_0 conda-forge
decorator 4.4.2 py_0 conda-forge
defusedxml 0.6.0 py_0 conda-forge
entrypoints 0.3 py36h9f0ad1d_1001 conda-forge
git 2.27.0 0 conda-forge
idna 2.9 py_1 conda-forge
importlib-metadata 1.6.1 py36h9f0ad1d_0 conda-forge
importlib_metadata 1.6.1 0 conda-forge
ipykernel 5.3.0 py36h5ca1d4c_0 conda-forge
ipython 7.15.0 py36h9f0ad1d_0 conda-forge
ipython_genutils 0.2.0 py_1 conda-forge
jedi 0.17.0 py36h9f0ad1d_0 conda-forge
jinja2 2.11.2 pyh9f0ad1d_0 conda-forge
jinja2-time 0.2.0 py_2 conda-forge
json5 0.9.4 pyh9f0ad1d_0 conda-forge
jsonschema 3.2.0 py36h9f0ad1d_1 conda-forge
jupyter_client 6.1.3 py_0 conda-forge
jupyter_core 4.6.3 py36h9f0ad1d_1 conda-forge
jupyterlab 2.1.4 py_1 conda-forge
jupyterlab_server 1.1.5 py_0 conda-forge
libsodium 1.0.17 h2fa13f4_0 conda-forge
markupsafe 1.1.1 py36h68a101e_1 conda-forge
mistune 0.8.4 py36h68a101e_1001 conda-forge
nbconvert 5.6.1 py36h9f0ad1d_1 conda-forge
nbformat 5.0.6 py_0 conda-forge
nodejs 14.4.0 0 conda-forge
notebook 4.4.1 py36_0 conda-forge
openssl 1.1.1g he774522_0
packaging 20.4 pyh9f0ad1d_0 conda-forge
pandoc 0 conda-forge
pandocfilters 1.4.2 py_1 conda-forge
parso 0.7.0 pyh9f0ad1d_0 conda-forge
pickleshare 0.7.5 py36h9f0ad1d_1001 conda-forge
pip 20.1.1 py_1 conda-forge
poyo 0.5.0 py_0 conda-forge
prompt-toolkit 3.0.5 py_0 conda-forge
pycparser 2.20 py_0 conda-forge
pygments 2.6.1 py_0 conda-forge
pyopenssl 19.1.0 py_1 conda-forge
pyparsing 2.4.7 pyh9f0ad1d_0 conda-forge
pyrsistent 0.16.0 py36h68a101e_0 conda-forge
pysocks 1.7.1 py36h9f0ad1d_1 conda-forge
python 3.6.10 he025d50_1009_cpython conda-forge
python-dateutil 2.8.1 py_0 conda-forge
python-slugify 4.0.0 pyh9f0ad1d_1 conda-forge
python_abi 3.6 1_cp36m conda-forge
pywin32 227 py36hfa6e2cd_0 conda-forge
pyzmq 19.0.1 py36h274d426_0 conda-forge
requests 2.23.0 pyh8c360ce_2 conda-forge
setuptools 47.3.1 py36h9f0ad1d_0 conda-forge
six 1.15.0 pyh9f0ad1d_0 conda-forge
testpath 0.4.4 py_0 conda-forge
text-unidecode 1.3 py_0 conda-forge
tornado 5.1.1 py36hfa6e2cd_0
traitlets 4.3.3 py36h9f0ad1d_1 conda-forge
unidecode 1.1.1 py_0 conda-forge
urllib3 1.25.9 py_0 conda-forge
vc 14.1 h869be7e_1 conda-forge
vs2015_runtime 14.16.27012 h30e32a0_2 conda-forge
wcwidth 0.2.4 pyh9f0ad1d_0 conda-forge
webencodings 0.5.1 py_1 conda-forge
wheel 0.34.2 py_1 conda-forge
whichcraft 0.6.1 py_0 conda-forge
win_inet_pton 1.1.0 py36_0 conda-forge
wincertstore 0.2 py36_1003 conda-forge
zeromq 4.3.2 h6538335_2 conda-forge
zipp 3.1.0 py_0 conda-forge

With tornado 5.1.1 I get end endless loop if these errors:

[E 09:33:34.905 LabApp] Uncaught exception GET /api/kernels/65c2fde1-acb6-4499-b623-4da5a0a78e4c/channels?session_id=428ffe7c-b9fb-4380-af54-e92540e851dc&token=f1789834874be11a289c5d2a784d0e6ea937cdbcfb90c16f (
HTTPServerRequest(protocol=‘http’, host=‘localhost:8888’, method=‘GET’, uri=’/api/kernels/65c2fde1-acb6-4499-b623-4da5a0a78e4c/channels?session_id=428ffe7c-b9fb-4380-af54-e92540e851dc&token=f1789834874be11a289c5d2a784d0e6ea937cdbcfb90c16f’, version=‘HTTP/1.1’, remote_ip=‘’)
Traceback (most recent call last):
File “C:\Users\user\miniconda3\envs\jl-ext\lib\site-packages\tornado\websocket.py”, line 546, in _run_callback
result = callback(*args, **kwargs)
File “C:\Users\user\miniconda3\envs\jl-ext\lib\site-packages\notebook\services\kernels\handlers.py”, line 260, in open
super(ZMQChannelsHandler, self).open()
File “C:\Users\user\miniconda3\envs\jl-ext\lib\site-packages\notebook\base\zmqhandlers.py”, line 176, in open
self.send_ping, self.ping_interval, io_loop=loop,
TypeError: init() got an unexpected keyword argument ‘io_loop’