[Python] Plotly Charts Not Displaying Correctly Despite Valid Data and Code

I'm facing a strange issue where none of my Plotly charts display correctly, even though the data is valid and the code runs without errors. This includes various chart types like line, bar, pie, and scatter charts.

Problem:

• The charts do render, but the data doesn't reflect correctly in the visuals.
• Sometimes the charts appear blank, misaligned, or show incorrect values.
• There are no errors in the console or traceback, which makes debugging hard.

Context: I'm using Plotly with Flask in a web app. The charts are passed to the frontend using plotly.utils.PlotlyJSONEncoder and rendered using Plotly.newPlot() in JavaScript. Here’s an example of how I generate and pass a chart:

Python (Flask backend):

import json
import plotly.graph_objs as go
from flask import render_template

@app.route("/weather")
def weather():
fig = go.Figure(data=go.Bar(x=["Mon", "Tue", "Wed"], y=[2, 5, 3]))
graphJSON = json.dumps(fig, cls=plotly.utils.PlotlyJSONEncoder)
return render_template("weather.html", graphJSON=graphJSON)


HTML (Jinja + JavaScript frontend):

<div id="plot"></div>
<script>
var graph = {{ graphJSON | safe }};
Plotly.newPlot("plot", graph.data, graph.layout);
</script>


What I tried:

• Validated all x and y values are lists of the same length
• Tried fig.to_json() instead of json.dumps()
• Made sure graph.data and graph.layout are being accessed properly
• Filled NaN values with 0
• Checked for browser console errors (none found)
• Verified Plotly is correctly loaded from CDN

What I expected:

Charts should render based on the data e.g., bar charts with correct heights, pie charts with correct slices, and heatmaps with accurate density. Instead, the visuals don't align with the actual data, or appear empty or broken.

Expected Output (when using .show() in Python) (https://i.sstatic.net/gzRyqWIz.png)

Actual Output (on the webpage via Flask and Plotly.newPlot())(https://i.sstatic.net/KIf5eUGy.png)

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