Getting Vertical lines while plotting multiple line plots in dash

I’m facing issue with mutiple line plot in Dash, actually it is showing some unnecessary vertical line sometime opposite to my data.
I’m adding the code and image below.

cols = ['col1', 'col2']
m_data = [
                'x': data['date'],
                'y': data[col],
            for col in cols[:2]

        return {"data": m_data, layout={} }