Cannot save notebook on VPN when pyviz/hvplot or bokeh have outputs

I understand that this, at first glance, doesn't sound like a pyviz/hvplot or bokeh issue, but I ask that you hear me out and watch the screencast before judging.

The issue I'm facing is that when I have hvplot or bokeh outputs in my notebook, I am suddenly unable to save my notebook when connected to my company VPN. I have gone back-and-forth with our networking team, and when I finally narrowed down the issue, it turned out the minimal reproducible example was the one in the screencast.

This notebook cell would have no issues:

```python
%%capture
import hvplot.pandas
import holoviews as hv

hv.extension("bokeh")
```

While this notebook cell would cause issues with saving:

```python
import hvplot.pandas
import holoviews as hv

hv.extension("bokeh")
```

The only difference is whether or not I capture the output.

UPDATE: it also doesn't matter if I have hvplot graphics displaying in the notebook or not - only that first cell is an issue.

#### ALL software version info (hvPlot, holoviews, bokeh, python, notebook, OS, browser, any other relevant packages)

hvplot: 0.4.0
bokeh: 1.3.0
python: 3.7
jupyterlab: 1.0.2
jupyterlab_server: 1.0.0
jupyter: 1.0.0

Browser: Chrome 75.0.3770.142
OS: macOS 10.14.5

#### Stack traceback and/or browser JavaScript console output

Please see screencast for this.

#### Screenshots or screencasts of the bug in action

Screencast: https://drive.google.com/file/d/1ZI8AErWtU-7ZdwyranCOh205ykCgFCha/view?usp=sharing