It looks like something is wrong with the way you are formatting the data. I just release a new version (0.0.15) of the dash-extensions, which contains performance improvements and syntax sugar,
For your particular case, with the new version, i guess you could do something like,
...
from dash_extensions.download import send_data_frame
df = pd.DataFrame(async_job)
dff = df[new_col_list]
report_name = 'facebook_{}.csv'.format(datetime.datetime.now().strftime("%Y_%m_%d-%H_%M_%S"))
return send_data_frame(dff.to_csv, report_name)