Plotly express line chart not showing lines

Any ideas why this would happen?

Iโ€™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 arenโ€™t plotted but when using native (Fedora Server) systemd service to run gunicorn then lines are plotted.
This has given me nightmares.