Uncaught ModuleNotFoundError: No module named 'matplotlib.pyplot'

[areithofer]

Couldn't load plugin 'VoGisProfilTool' due to an error when calling its classFactory() method
Steps to reproduce

1. First
2. Second
3. Third

Traceback (most recent call last):
  File "C:/OSGEO4~1/apps/qgis-ltr/./python\qgis\utils.py", line 335, in startPlugin
    plugins[packageName] = package.classFactory(iface)
  File "C:/Users/user9/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\VoGisProfilTool\__init__.py", line 26, in classFactory
    from VoGisProfilTool.vogisprofiltoolmain import VoGISProfilToolMain
  File "C:/OSGEO4~1/apps/qgis-ltr/./python\qgis\utils.py", line 685, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:/Users/user9/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\VoGisProfilTool\vogisprofiltoolmain.py", line 31, in <module>
    from VoGisProfilTool.vogisprofiltoolmaindialog import VoGISProfilToolMainDialog
  File "C:/OSGEO4~1/apps/qgis-ltr/./python\qgis\utils.py", line 685, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:/Users/user9/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\VoGisProfilTool\vogisprofiltoolmaindialog.py", line 34, in <module>
    from VoGisProfilTool.vogisprofiltoolplot import VoGISProfilToolPlotDialog
  File "C:/OSGEO4~1/apps/qgis-ltr/./python\qgis\utils.py", line 685, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:/Users/user9/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\VoGisProfilTool\vogisprofiltoolplot.py", line 31, in <module>
    import matplotlib.pyplot as plt
  File "C:/OSGEO4~1/apps/qgis-ltr/./python\qgis\utils.py", line 685, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
ModuleNotFoundError: No module named 'matplotlib.pyplot'

VoGisProfilTool 3.0.2, QGIS 3.4.9-Madeira on Windows 10