This issue was first reported in #891, but it doesn't seem like it was fully understood or addressed. I found another post on the community forums about the same thing at https://community.plot.ly/t/solved-symbol-changes-not-showing-up-with-scattermapbox/1638

I am able to use only a subset of the icons found on https://labs.mapbox.com/maki-icons/. When I use "bus" or "embasssy" as the symbol, I see the icon without issue. When I change the symbol to "home" or "wheelchair", the icon is not rendered. It's as though only a subset of the mapbox icons are actually available. An excerpt from my code is copied below. This is intended to show a "wheelchair" icon, but it does not appear to work.

        vehicle_fig.add_trace(go.Scattermapbox(
            name='Stop',
            lat=stop_lat,
            lon=stop_lon,
            mode='markers',
            marker=go.scattermapbox.Marker(
                size=15,
                symbol='wheelchair'
            ),
            showlegend=False,
            text=stop_address,
            hoverinfo='text',
            hoverlabel=dict(bgcolor='#735139',
                            font=dict(color='white',
                                      size=20))
        ))