A connection to the notebook server could not be established.

[mareq]

Jupyter keeps reporting the problem about being unable to connect to kernel:

A connection to the notebook server could not be established. The notebook will continue trying to reconnect. Check your network connection or notebook server configuration.

I have followed the steps from the readme file, tried to downgrade tornado as per this stackoverflow response and I am running on Debian testing:

$ python --version
Python 3.7.3
$ jupyter --version
jupyter core     : 4.5.0
jupyter-notebook : 5.7.4
qtconsole        : 4.4.3
ipython          : 7.3.0
ipykernel        : 5.1.0
jupyter client   : 5.3.3
jupyter lab      : not installed
nbconvert        : 5.4.1
ipywidgets       : 7.4.2
nbformat         : 4.4.0
traitlets        : 4.3.2
$ conda list
# packages in environment at /home/<my-username>/.conda/envs/scijava:
#
# Name                    Version                   Build  Channel
_libgcc_mutex             0.1                        main
asn1crypto                1.2.0                    py37_0    conda-forge
atomicwrites              1.3.0                      py_0    conda-forge
attrs                     19.3.0                     py_0    conda-forge
backcall                  0.1.0                      py_0    conda-forge
beakerx                   1.4.0                    py37_0    conda-forge
bleach                    3.1.0                      py_0    conda-forge
bzip2                     1.0.8                h516909a_1    conda-forge
ca-certificates           2019.10.16                    0
certifi                   2019.9.11                py37_0
cffi                      1.13.1           py37h8022711_0    conda-forge
chardet                   3.0.4                 py37_1003    conda-forge
cloudpickle               1.2.2                      py_0    conda-forge
cryptography              2.7              py37h72c5cf5_0    conda-forge
cycler                    0.10.0                     py_2    conda-forge
cytoolz                   0.10.0           py37h516909a_0    conda-forge
dask-core                 2.6.0                      py_0    conda-forge
dbus                      1.13.6               he372182_0    conda-forge
decorator                 4.4.0                      py_0    conda-forge
defusedxml                0.6.0                      py_0    conda-forge
entrypoints               0.3                   py37_1000    conda-forge
expat                     2.2.5             he1b5a44_1004    conda-forge
fontconfig                2.13.1            h86ecdb6_1001    conda-forge
freetype                  2.10.0               he983fc9_1    conda-forge
gettext                   0.19.8.1          hc5be6a0_1002    conda-forge
glib                      2.58.3            h6f030ca_1002    conda-forge
gst-plugins-base          1.14.5               h0935bb2_0    conda-forge
gstreamer                 1.14.5               h36ae1b5_0    conda-forge
icu                       64.2                 he1b5a44_1    conda-forge
idna                      2.8                   py37_1000    conda-forge
imageio                   2.6.1                    py37_0    conda-forge
imglyb                    0.3.5            py37h5ca1d4c_0    conda-forge
importlib_metadata        0.23                     py37_0    conda-forge
ipykernel                 5.1.3            py37h5ca1d4c_0    conda-forge
ipython                   7.8.0            py37h5ca1d4c_0    conda-forge
ipython_genutils          0.2.0                      py_1    conda-forge
ipywidgets                7.5.1                      py_0    conda-forge
jedi                      0.15.1                   py37_0    conda-forge
jgo                       0.4.0                    py37_0    conda-forge
jinja2                    2.10.3                     py_0    conda-forge
jpeg                      9c                h14c3975_1001    conda-forge
jsonschema                3.1.1                    py37_0    conda-forge
jupyter                   1.0.0                    py37_7
jupyter_client            5.3.3                    py37_1    conda-forge
jupyter_console           6.0.0                      py_0    conda-forge
jupyter_contrib_core      0.3.3                      py_2    conda-forge
jupyter_contrib_nbextensions 0.5.1                    py37_0    conda-forge
jupyter_core              4.5.0                      py_0    conda-forge
jupyter_highlight_selected_word 0.2.0                 py37_1000    conda-forge
jupyter_latex_envs        1.4.4                 py37_1000    conda-forge
jupyter_nbextensions_configurator 0.4.1                    py37_0    conda-forge
kiwisolver                1.1.0            py37hc9558a2_0    conda-forge
libblas                   3.8.0               14_openblas    conda-forge
libcblas                  3.8.0               14_openblas    conda-forge
libclang                  9.0.0                hc9558a2_1    conda-forge
libffi                    3.2.1             he1b5a44_1006    conda-forge
libgcc-ng                 9.1.0                hdf63c60_0
libgfortran-ng            7.3.0                hdf63c60_2    conda-forge
libiconv                  1.15              h516909a_1005    conda-forge
liblapack                 3.8.0               14_openblas    conda-forge
libllvm9                  9.0.0                hc9558a2_2    conda-forge
libopenblas               0.3.7                h6e990d7_2    conda-forge
libpng                    1.6.37               hed695b0_0    conda-forge
libsodium                 1.0.17               h516909a_0    conda-forge
libstdcxx-ng              9.1.0                hdf63c60_0
libtiff                   4.0.10            hfc65ed5_1004    conda-forge
libuuid                   2.32.1            h14c3975_1000    conda-forge
libxcb                    1.13              h14c3975_1002    conda-forge
libxkbcommon              0.9.1                hebb1f50_0    conda-forge
libxml2                   2.9.9                hee79883_5    conda-forge
libxslt                   1.1.33               h31b3aaa_0    conda-forge
lxml                      4.4.1            py37h7ec2d77_0    conda-forge
lz4-c                     1.8.3             he1b5a44_1001    conda-forge
markupsafe                1.1.1            py37h14c3975_0    conda-forge
matplotlib                3.1.1                    py37_1    conda-forge
matplotlib-base           3.1.1            py37he7580a8_1    conda-forge
maven                     3.6.0                         0    conda-forge
mistune                   0.8.4           py37h14c3975_1000    conda-forge
more-itertools            7.2.0                      py_0    conda-forge
nbconvert                 5.6.1                    py37_0    conda-forge
nbformat                  4.4.0                      py_1    conda-forge
ncurses                   6.1               hf484d3e_1002    conda-forge
networkx                  2.4                        py_0    conda-forge
notebook                  5.7.8                    py37_0
nspr                      4.23                 he1b5a44_0    conda-forge
nss                       3.47                 he751ad9_0    conda-forge
numpy                     1.17.3           py37h95a1406_0    conda-forge
olefile                   0.46                       py_0    conda-forge
openjdk                   8.0.192           h14c3975_1003    conda-forge
openssl                   1.1.1d               h7b6447c_3
packaging                 19.2                       py_0    conda-forge
pandas                    0.25.2           py37hb3f55d8_0    conda-forge
pandoc                    2.7.3                         0    conda-forge
pandocfilters             1.4.2                      py_1    conda-forge
parso                     0.5.1                      py_0    conda-forge
pcre                      8.43                 he1b5a44_0    conda-forge
pexpect                   4.7.0                    py37_0    conda-forge
pickleshare               0.7.5                 py37_1000    conda-forge
pillow                    6.2.1            py37h6b7be26_0    conda-forge
pip                       19.3.1                   py37_0    conda-forge
pluggy                    0.13.0                   py37_0    conda-forge
prometheus_client         0.7.1                      py_0    conda-forge
prompt_toolkit            2.0.10                     py_0    conda-forge
psutil                    5.6.3            py37h516909a_0    conda-forge
pthread-stubs             0.4               h14c3975_1001    conda-forge
ptyprocess                0.6.0                   py_1001    conda-forge
py                        1.8.0                      py_0    conda-forge
py4j                      0.10.8.1                   py_0    conda-forge
pycparser                 2.19                     py37_1    conda-forge
pygments                  2.4.2                      py_0    conda-forge
pyimagej                  0.4.0                 py37_1001    conda-forge
pyjnius                   1.2.0            py37h93af967_0    conda-forge
pyopenssl                 19.0.0                   py37_0    conda-forge
pyparsing                 2.4.2                      py_0    conda-forge
pyqt                      5.12.3           py37hcca6a23_0    conda-forge
pyqt5-sip                 4.19.18                  pypi_0    pypi
pyqtwebengine             5.12.1                   pypi_0    pypi
pyrsistent                0.15.4           py37h516909a_0    conda-forge
pysocks                   1.7.1                    py37_0    conda-forge
pytest                    5.2.2                    py37_0    conda-forge
python                    3.7.3                h33d41f4_1    conda-forge
python-dateutil           2.8.0                      py_0    conda-forge
pytz                      2019.3                     py_0    conda-forge
pywavelets                1.1.1            py37hc1659b7_0    conda-forge
pyyaml                    5.1.2            py37h516909a_0    conda-forge
pyzmq                     18.1.0           py37h1768529_0    conda-forge
qt                        5.12.5               h0c104cb_0    conda-forge
qtconsole                 4.5.5                      py_0    conda-forge
readline                  8.0                  hf8c457e_0    conda-forge
requests                  2.22.0                   py37_1    conda-forge
rise                      5.5.1                    py37_0    conda-forge
scikit-image              0.16.2           py37hb3f55d8_0    conda-forge
scipy                     1.3.1            py37h921218d_2    conda-forge
scyjava                   0.2.3                    py37_0    conda-forge
send2trash                1.5.0                      py_0    conda-forge
setuptools                41.4.0                   py37_0    conda-forge
six                       1.12.0                py37_1000    conda-forge
sqlite                    3.30.1               hcee41ef_0    conda-forge
terminado                 0.8.2                    py37_0    conda-forge
testpath                  0.4.2                   py_1001    conda-forge
tk                        8.6.9             hed695b0_1003    conda-forge
toolz                     0.10.0                     py_0    conda-forge
tornado                   4.5.3                    py37_0
traitlets                 4.3.3                    py37_0    conda-forge
urllib3                   1.25.6                   py37_0    conda-forge
wcwidth                   0.1.7                      py_1    conda-forge
webencodings              0.5.1                      py_1    conda-forge
wheel                     0.33.6                   py37_0    conda-forge
widgetsnbextension        3.5.1                    py37_0    conda-forge
xorg-libxau               1.0.9                h14c3975_0    conda-forge
xorg-libxdmcp             1.1.3                h516909a_0    conda-forge
xz                        5.2.4             h14c3975_1001    conda-forge
yaml                      0.1.7             h14c3975_1001    conda-forge
zeromq                    4.3.2                he1b5a44_2    conda-forge
zipp                      0.6.0                      py_0    conda-forge
zlib                      1.2.11            h516909a_1006    conda-forge
zstd                      1.4.3                h3b9ef0a_0    conda-forge

Am I doing something wrong?