Html export go.FigureWidget() not working

I experience an error when I try to export a jupyterlab notebook to html (by File > Save and export notebook as > HTML).
I enabled ‘save widget state’ and saved the notebook first.

Exporting a notebook to html with a ‘normal’ ploty figure works fine.

But exporting a notebook to html with a plotly figure widget results in nothing, .

I tried this in two different installations (windows & linux based).
Is this a bug or could I fix this with some configuration?

plotly 5.10.0
nbconvert 6.5.0
jupyterhub 1.5.0
jupyterlab 3.4.3
ipywidgets 7.7.0

could someone reproduce this bug?