Trendline is missing from the scatter plot

Not sure if this is bug or misconfiguration, I attempt to plot the dots with trendline added, but it just fails to show up in the figure. My code is written as follows:

import os
import pandas as pd
import as px

df = pd.read_json('general.json')

# Plot median solved time against mean solved time for each topic using count ratio as size
fig = px.scatter(df_topics, y="Challenge median solved time", x="Challenge mean solved time",
                 color="Challenge topic", hover_name="Challenge topic", size="Challenge count", trendline="ols")
    margin=dict(l=0, r=0, t=0, b=0))
fig.write_image('Challenge median vs mean solved time.png')

The output figure looks like this:

Any idea what I should do with it?