Error in warning message "The following plotters have already been defined"

Hello,

We are seeing a weird error when trying to import psyplot, it seems the code crash while trying to display a warning regarding "plotters have already been defined":

(climate_science) $ python
Python 3.9.1 | packaged by conda-forge | (default, Jan 26 2021, 01:34:10) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import psyplot.project as psy
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/.../anaconda-py3/2020.11/envs/climate_science/lib/python3.9/site-packages/psyplot/__init__.py", line 64, in <module>
    rcParams.load_plugins()
  File "/.../anaconda-py3/2020.11/envs/climate_science/lib/python3.9/site-packages/psyplot/config/rcsetup.py", line 852, in load_plugins
    msg = ("Error while loading psyplot plugin %s! The "
TypeError: not all arguments converted during string formatting

I am not sure why the warning is displayed in the first place. The error itself seems to happen because "%s" % ep is not valid (at least with Python 3.9).

Here is the list of installed psyplot-related Conda packages:

(climate_science) $ conda list | grep psy
psy-maps                  1.4.2            py39hf3d152e_2    conda-forge
psy-reg                   1.4.0            py39hf3d152e_3    conda-forge
psy-simple                1.4.1            py39hf3d152e_2    conda-forge
psy-view                  0.2.0            py39hf3d152e_1    conda-forge
psyplot                   1.4.3            py39hf3d152e_1    conda-forge
psyplot-gui               1.4.0            py39hf3d152e_2    conda-forge

Best regards, Rémi