title: Plotly displaying sad 'fail' face instead of output
body: <p>I'm using <code>plotly==4.5.1</code> in a <code>jupyter==1.0.0</code> notebook, <code>python==3.7.4</code>. </p>
  
  <p>The same piece of code which previous showed this:</p>
  
  <p><a href="https://i.stack.imgur.com/Y1cta.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/Y1cta.jpg" alt="plotly success"></a></p>
  
  <p>Is now showing this, without having had any modifications:</p>
  
  <p><a href="https://i.stack.imgur.com/rAHX1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/rAHX1.png" alt="plotly fail"></a></p>
  
  <p>Does anyone have any insights over why this might be? Is it something to do with plotly's online/offline modes?</p>
  
  <p>For completeness, here is some example dummy data </p>
  
  <pre><code>df_heat = pd.DataFrame({'lat': {0: -62.884215, 1: -62.834226, 2: -62.811707, 3: -62.744564, 4: -62.704835},
   'lon': {0: 39.4402361, 1: 39.4080722, 2: 39.3804616, 3: 39.4891116, 4: 39.4243305},
   'count': {0: 1, 1: 1, 2: 1, 3: 1, 4: 1}})
  </code></pre>
  
  <p>And the code used to create the map.</p>
  
  <pre><code>import plotly.graph_objects as go
  
  fig = go.Figure(go.Densitymapbox(lat=df_heat['lat'], lon=df_heat['lon'], z=df_heat['count'],
                                   radius=10,))
  fig.update_layout(mapbox_style="carto-positron", mapbox_zoom=10, mapbox_center = {"lat": 40.7831, "lon": -73.9712},)
  
  fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})
  fig.show()
  </code></pre>
  
  <h2>Update (before any answers were posted)</h2>
  
  <p>Restarting my computer seemed to solve this issue ¯\_(ツ)_/¯. Insight on why it happened would still be appreciated.</p>