The bokeh graph is not displaying in Jupyter. It just says "Loading BokehJS ..."

I log in with the jupyter notebook, and open two books. The script that I show below (as an example), in one of the notebooks shows me the image correctly. In the other it shows me the message "Loading BokehJS …"

import numpy as np
# bokeh basics
from bokeh.plotting import figure
from bokeh.io import show, output_notebook

x = [1,2,3,4,5]
y = [2,4,6,8,10]
#output_file('line.html')
fig = figure(title = 'Line Plot example', x_axis_label = 'x', y_axis_label = 'y')
fig.line(x,y)

# Set to output the plot in the notebook
output_notebook()
show(fig)

What can be the cause of this problem? Could it be related to the fact that the first thing I ran was this program but using the output_file () function to store the output in an HTML file? How can I avoid this problem?

Information taken with! Bokeh info

Python version      :  3.8.3 (default, Jul  2 2020, 16:21:59) 
IPython version     :  7.16.1
Tornado version     :  6.0.4
Bokeh version       :  2.1.1
BokehJS static path :  /home/enri/anaconda3/envs/plotly/lib/python3.8/site-packages/bokeh/server/static
node.js version     :  (not installed)
npm version         :  (not installed)

That happens to me too - comment out the output-file stuff and choose restart kernel and clear outputs. It works the next time around for me.

I solved the problem by starting like this:
from bokeh.plotting import reset_output
reset_output ()

import pandas_bokeh
pandas_bokeh.output_notebook()

Thanks