MS Edge (non-Chromium): jupyter-matplotlib plots not showing in JupyterLab

Hello, this is my first GitHub post. I just installed ipympl and can't get it to work properly in JupyterLab. The widget controls are there, but plot is blank. Plot coordinates are updated when mouse is moved around in the plot area. It works fine in Jupyter notebooks.

Setup (Win 10 x64, Anaconda):

conda list jupyter
# packages in environment at C:\Users\me\Anaconda3\envs\jupmpl:
#
# Name                    Version                   Build  Channel
jupyter                   1.0.0                    py37_7
jupyter_client            5.3.4                    py37_0
jupyter_console           6.1.0                      py_0
jupyter_core              4.6.1                    py37_0
jupyterlab                1.2.6              pyhf63ae98_0
jupyterlab_server         1.0.6                      py_0
jupyterthemes             0.20.0                   pypi_0    pypi

jupyter labextension list
JupyterLab v1.2.6
Known labextensions:
   app dir: C:\Users\me\Anaconda3\envs\jupmpl\share\jupyter\lab
        @bokeh/jupyter_bokeh v1.1.1 enabled  ok
        @jupyter-widgets/jupyterlab-manager v1.1.0 enabled  ok
        jupyter-matplotlib v0.5.0 enabled  ok

conda -V
conda 4.8.2

conda list 'python|conda|ipympl|nodejs|ipywidgets|widgetsnbextension|notebook|matplotlib'
# packages in environment at C:\Users\me\Anaconda3\envs\jupmpl:
#
# Name                    Version                   Build  Channel
_anaconda_depends         2019.03                  py37_0
anaconda                  custom                   py37_1
anaconda-client           1.7.2                    py37_0
anaconda-navigator        1.9.7                    py37_0
anaconda-project          0.8.4                      py_0
conda-package-handling    1.6.0            py37h62dcd97_0
conda-verify              3.4.2                      py_1
ipympl                    0.4.1                      py_0    conda-forge
ipython                   7.12.0           py37h5ca1d4c_0
ipython_genutils          0.2.0                    py37_0
ipywidgets                7.5.1                      py_0
matplotlib                3.1.3                    py37_0
matplotlib-base           3.1.3            py37h64f37c6_0
msgpack-python            0.6.1            py37h74a9793_1
msys2-conda-epoch         20160418                      1
nodejs                    13.8.0                        0    conda-forge
notebook                  6.0.3                    py37_0
python                    3.7.6                h60c2a47_2
python-dateutil           2.8.1                      py_0
python-libarchive-c       2.8                     py37_13
widgetsnbextension        3.5.1                    py37_0

I followed install directions as on the jupyterlab-matplotlib GitHub site, and am using the matplotlib Jupyter magic:

%matplotlib widget

Note that I can get working interactive 3d plots in external windows by invoking %pylab or
%matplotlib from JupyterLab. But I get no plots inline.

I have messed around with this for many hours and am getting nowhere. Any help would be greatly appreciated! :-)

Beginne damit, den leeren Inline-Plot in JupyterLab 1.2.6 auf nicht auf Chromium basierendem Microsoft Edge mit den gemeldeten Versionen von ipympl, matplotlib und jupyter-matplotlib zu reproduzieren. Vergleiche dasselbe %matplotlib widget-Beispiel in Jupyter Notebook und untersuche den Erweiterungs- und Widget-Rendering-Pfad von JupyterLab. Als erledigt gilt die Aufgabe, wenn der Plot in der betroffenen Umgebung inline mit funktionierenden Steuerelementen gerendert wird.