Plotly express line chart not showing lines

Any ideas why this would happen?

I’ve checked that the dataframe has the relevant data and everything is there.

        df = pd.read_json('static/data-sources/data.json')
        df.sort_values(by='TIMESTAMP', inplace=True)
        # print(df)
        fsdf = df.loc[df['HOSTNAME'] == 'prod1']
        # print(fsdf)
        fsdf.drop(fsdf[fsdf['FILESYSTEM'] == 'ERROR'].index, inplace=True)
        fig = px.line(fsdf, x="TIMESTAMP", y="PERCENTAGE",
                      color="FILESYSTEM",
                      template="plotly_white"
                      )
        fig.update_layout(
            title='Production Node 1',
            width=1010,
            height=600,
            font_family="Lato",
        )
        fig.update_xaxes(title='Date', tickmode='linear', tickangle=45,
                         tickfont=dict(family='Lato', size=12))
        fig.update_yaxes(title='Percentage Used', ticksuffix=' %', range=[0, 100])
        fig.write_image("static/images/filesystems-node1.svg")

Lines get plotted on local development server but not on production server.

So turns out when using supervisorctl to manage gunicorn service then lines aren’t plotted but when using native (Fedora Server) systemd service to run gunicorn then lines are plotted.
This has given me nightmares.