A connection to the notebook server could not be established.

Nobody has claimed this yet.

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](https://stackoverflow.com/a/52824269/5292184) 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//.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?

Start with the README setup steps and reproduce the notebook-server connection failure in the reported Debian testing, Python 3.7.3, and Jupyter environment. Inspect the server and kernel connection logs to identify the failing component; done means the cause is isolated and a verified fix or documented configuration change prevents the reconnect message.

Written by the indexing model from the issue text.