[Cross-Post Bug] Degraded performance with Bokeh 2.4.0 and Panel

I’m not sure if this issue is specific to just Bokeh or if Panel adds to it, but after upgrading to Bokeh 2.4.0, I’ve been seeing massively degraded performance in quadmeshes & heatmaps when serving pre-rendered charts via Panel HTML pane embeddings.

The left side shows the pre-rendered chart as standalone html file, while the right side shows the same pre-rendered chart embedded via Panel HTML pane.

This used to work fine before the update to 2.4.0.

Was also reported here:


Seems like the same issue is also present in Jupyterlab.

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Sounds like this unfortunate regression has already been fixed in bokeh and will be included in Bokeh 2.4.1