[Dúvida] Erro plot_diagnostics

Olá pessoal,

Estou tendo o seguinte erro ao executar a seguinte linha de comando:

results.plot_diagnostics(figsize=(16,8))
plt.show()

Erro:

TypeError                                 Traceback (most recent call last)
<ipython-input-34-6a31db76aed6> in <module>
----> 1 results.plot_diagnostics(figsize=(16,8))
      2 plt.show()

C:\ProgramData\Anaconda3\lib\site-packages\statsmodels\tsa\statespace\mlemodel.py in plot_diagnostics(self, variable, lags, fig, figsize)
   3900         else:
   3901             x = np.arange(len(resid))
-> 3902         ax.plot(x, resid)
   3903         ax.hlines(0, x[0], x[-1], alpha=0.5)
   3904         ax.set_xlim(x[0], x[-1])

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\axes\_axes.py in plot(self, scalex, scaley, data, *args, **kwargs)
   1665         lines = [*self._get_lines(*args, data=data, **kwargs)]
   1666         for line in lines:
-> 1667             self.add_line(line)
   1668         self.autoscale_view(scalex=scalex, scaley=scaley)
   1669         return lines

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\axes\_base.py in add_line(self, line)
   1900             line.set_clip_path(self.patch)
   1901 
-> 1902         self._update_line_limits(line)
   1903         if not line.get_label():
   1904             line.set_label('_line%d' % len(self.lines))

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\axes\_base.py in _update_line_limits(self, line)
   1922         Figures out the data limit of the given line, updating self.dataLim.
   1923         """
-> 1924         path = line.get_path()
   1925         if path.vertices.size == 0:
   1926             return

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\lines.py in get_path(self)
   1025         """
   1026         if self._invalidy or self._invalidx:
-> 1027             self.recache()
   1028         return self._path
   1029 

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\lines.py in recache(self, always)
    668         if always or self._invalidx:
    669             xconv = self.convert_xunits(self._xorig)
--> 670             x = _to_unmasked_float_array(xconv).ravel()
    671         else:
    672             x = self._x

C:\ProgramData\Anaconda3\lib\site-packages\matplotlib\cbook\__init__.py in _to_unmasked_float_array(x)
   1388         return np.ma.asarray(x, float).filled(np.nan)
   1389     else:
-> 1390         return np.asarray(x, float)
   1391 
   1392 

TypeError: float() argument must be a string or a number, not 'Timestamp'

Obs.: Executei o código upado no Git e dá o mesmo erro. Estou usando o python 3.9.