Bokeh rendering bug of correctly nested composite object


I am having troubles understanding why the following holoviews object structure cannot be rendered using bokeh:

:NdLayout   [dim1]
   :HoloMap   [dim2]
         .Scatter.I  :Scatter   [a]   (b)
         .Scatter.II :Scatter   [a]   (b,c)

If I try to export it to a static HTML file using, I get the following error:

AbbreviatedException: expected an element of either Seq(String), Seq(Tuple(String, String)) or Seq(Tuple(String, String, String)), got [nan]

Anyone has any idea of how I could get this to work?

The composite object was generated with code looking like that:

df1=pandas.DataFrame({'dim1':[3,4,5], 'dim2':[1,1,2], 'a':[1,2,3], 'b':[1,2,3], 'c':[1,2,3]})
scatter1=df1.hvplot.scatter(x='a', y='b', c='c')
scatter2=df2.hvplot.scatter(x='a', y='b', c='grey')'dim1'), 'object.html') # this works

composite_object = (scatter1*scatter2).collate().layout('dim1') # holoviews will create a slider to explore 'dim2', implicitly

Thanks for your help!