ipywidgets_bokeh not loading ipython

[ncvangilse]

When instantiating a MatplotlibPane in Panel, I get an attribute error.

import panel as pn
from matplotlib import pyplot as plt

fig, ax = plt.subplots()
ax.plot([0,1,2], [2,2,4])
pn.pane.plot.Matplotlib(fig, interactive=True).show()

Raises

...
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/panel/pane/plot.py", line 170, in _get_widget
    from ipympl.backend_nbagg import FigureManager, Canvas, is_interactive
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/ipympl/__init__.py", line 27, in <module>
    matplotlib.use('module://ipympl.backend_nbagg')
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/matplotlib/__init__.py", line 1080, in use
    plt.switch_backend(name)
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/matplotlib/pyplot.py", line 277, in switch_backend
    class backend_mod(matplotlib.backend_bases._Backend):
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/matplotlib/pyplot.py", line 278, in backend_mod
    locals().update(vars(importlib.import_module(backend_name)))
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/home/jovyan/conda-envs/pmat/lib/python3.9/site-packages/ipympl/backend_nbagg.py", line 431, in <module>
    ip.events.register('post_execute', flush_figures)
AttributeError: 'NoneType' object has no attribute 'events'

I have tried implementing the pull request suggested in https://discourse.holoviz.org/t/matplotlib-pane-throwing-attributeerror-when-interactive-true/2911/6

but then I get errors:

ERROR:fake:Invalid Message
Traceback (most recent call last):
  File "C:\Users\nchvg\Miniconda3\envs\optisoil-engineering-tools\lib\site-packages\ipykernel\kernelbase.py", line 312, in dispatch_shell
    msg = self.session.deserialize(msg, content=True, copy=False)
  File "C:\Users\nchvg\Miniconda3\envs\optisoil-engineering-tools\lib\site-packages\jupyter_client\session.py", line 1048, in deserialize
    raise ValueError("Duplicate Signature: %r" % signature)
ValueError: Duplicate Signature: b'9b25b08aacbdc8c77ef9f91368742482787dd5afe83a7a6872bb7f3e1366b335'

Here is my env:

bokeh                     2.4.0            py38haa244fe_0    conda-forge
ipykernel                 6.4.1            py38h595d716_0    conda-forge
ipympl                    0.8.0              pyhd8ed1ab_0    conda-forge
ipython                   7.28.0           py38h595d716_0    conda-forge
ipython_genutils          0.2.0                      py_1    conda-forge
ipywidgets                7.6.5              pyhd8ed1ab_0    conda-forge
ipywidgets-bokeh          1.2.1                    pypi_0    pypi
jupyter_client            7.0.6              pyhd8ed1ab_0    conda-forge
jupyter_core              4.8.1            py38haa244fe_0    conda-forge
jupyterlab_pygments       0.1.2              pyh9f0ad1d_0    conda-forge
jupyterlab_widgets        1.0.2              pyhd8ed1ab_0    conda-forge