Data frame with two categorical columns and one numerical column being passed to px.parallel_categories. Only one column gets visualized, no matter what is passed to dimensions: a single column, two columns, or no columns.
Data types changed to str and category, but no change.
Data:

Code:
px.parallel_categories(occupations_by_year, dimensions=['Main_jobs', 'Election year'], color = 'count')
Result:

Python 3.6
plotly==3.10.0
plotly-express==0.3.0