My parallel coordinates plot no longer shows line traces in color – all lines are one shade of gray even though the color scale (Jet) is shown. Now I see the same issue on the documentation page https://plot.ly/python/parallel-coordinates-plot/. The final plot has the Jet color scale and all gray lines. Sure looks like a bug…
Thanks for reporting! It looks like a bug to me too, I created an issue here: https://github.com/plotly/plotly.js/issues/3385