"x unified" Does not show all data info at same X

Environment:

Python 3.9.5
plotly.py v5.6.0
VS Code Jupyter Environment

How it is now

fig = px.scatter(result_df, x=[1, 2, 2, 3], y=[1, 2, 3, 4])
fig.update_traces(mode="markers", hovertemplate=None)
fig.update_layout(hovermode="x unified")
fig.show()

As shown above, the hover box only displayed 1 y-axis value.

How it should be

The hover box should display all y-axis values at the same X, even if they are the same type, in my example scatter plot.
As demonstrated in the document, plotly has the capability to show all values at the same X. But unfortunately it only works when there are another data dimension involved.

Start with the minimal Python reproduction using px.scatter, update_traces, and hovermode="x unified", then compare its behavior with the linked hover-text documentation. Investigate why repeated points at the same X produce only one Y value in the hover box. Done means the hover box displays every Y-axis value at that X for the example case.