[BUG]: marker.colorbar.tickfont.textcase='normal' blanks scattermap on initial render, but Plotly.restyle renders correctly

[ym-xie]

Description

When initializing a Plotly Scattermap figure with
marker.colorbar.tickfont.textcase='normal', the initial render can fail to draw the
OpenStreetMap tiles and map-layer geometry. The figure area is mostly blank, with only
right-side numeric tick labels and the OpenStreetMap attribution visible.

However, if the same base figure is rendered first and the same property value is
then applied dynamically through Plotly.restyle, the map renders correctly: the OSM
tiles appear, the blue filled map layer is visible, and the cyan marker is drawn.

The setting is accepted by plotly.py and emitted as a valid trace property, so this
appears to be an initial-render/update-time rendering discrepancy involving
Scattermap marker colorbar tick font defaults rather than an invalid Python-side
property assignment.

Screenshots/Video

Steps to reproduce

import io
import time

import plotly
import plotly.graph_objects as go
import plotly.io as pio
from PIL import Image, ImageChops
from playwright.sync_api import sync_playwright

print(f"Plotly version: {plotly.__version__}")


def make_fig():
    fig = go.Figure(
        go.Scattermap(
            mode="markers",
            lon=[-73.605],
            lat=[45.51],
            marker={"size": 20, "color": ["cyan"]},
        )
    )

    polygon = [
        [
            [
                [-73.62, 45.50],
                [-73.59, 45.50],
                [-73.59, 45.53],
                [-73.62, 45.53],
                [-73.62, 45.50],
            ]
        ]
    ]

    fig.update_layout(
        map={
            "style": "open-street-map",
            "center": {"lon": -73.6, "lat": 45.5},
            "zoom": 12,
            "layers": [
                {
                    "source": {
                        "type": "FeatureCollection",
                        "features": [
                            {
                                "type": "Feature",
                                "geometry": {
                                    "type": "MultiPolygon",
                                  "coordinates": polygon,
                                },
                            }
                        ],
                    },
                    "type": "fill",
                    "below": "traces",
                    "color": "royalblue",
                }
            ],
        },
        margin={"l": 0, "r": 0, "b": 0, "t": 0},
    )
    return fig


fig = make_fig()

# Screenshot 1 / plot1.png: set the value in Python before the first render.
fig.data[0].marker.colorbar.tickfont.textcase = "normal"
assert fig.data[0].marker.colorbar.tickfont.textcase == "normal"
print("Python-side tickfont JSON:", fig.data[0].marker.colorbar.tickfont.to_plotly_json())
html1 = pio.to_html(fig, full_html=True, include_plotlyjs="cdn")


# Screenshot 2 / plot2.png: render first, then apply the same value with JS.
fig.data[0].marker.colorbar.tickfont.textcase = None
html2 = pio.to_html(fig, full_html=True, include_plotlyjs="cdn")
restyle_script = """
<script>
window.addEventListener("DOMContentLoaded", () => {
    const plotEl = document.getElementsByClassName("plotly-graph-div")[0];
    setTimeout(() => {
        Plotly.restyle(plotEl, {"marker.colorbar.tickfont.textcase": "normal"}, [0]);
    }, 1000);
});
</script>
"""
html2 = html2.replace("</body>", restyle_script + "\n</body>")


with sync_playwright() as p:
    browser = p.chromium.launch(
        headless=True,
        args=["--no-sandbox", "--disable-dev-shm-usage", "--disable-gpu"],
    )
    page = browser.new_page(viewport={"width": 1200, "height": 800})

    page.set_content(html1)
    time.sleep(1.5)
    img1 = page.screenshot(path="plot1.png")

    page.set_content(html2)
    time.sleep(2.0)
    img2 = page.screenshot(path="plot2.png")

    browser.close()

diff = ImageChops.difference(
    Image.open(io.BytesIO(img1)).convert("RGB"),
    Image.open(io.BytesIO(img2)).convert("RGB"),
)

print("Saved plot1.png and plot2.png")
assert diff.getbbox() is not None, "Reproducer did not reproduce: images are identical."

Notes

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