There seems to be a breaking change between 6.2.0 and 6.3.0. When setting the top-margin to 0 the y-axis label is cut off when it is right at the end of the axis.

You can reproduce this with this code.

import plotly.graph_objects as go
from datetime import datetime
x = [datetime(1912, 5, 6, 0, 0), datetime(2019, 5, 10, 0, 0)]
y = [7.6, 23.9]
fig = go.Figure()
fig.add_trace(go.Scatter(x=x, y=y, mode='markers'))
fig.add_trace(go.Scatter(x=[datetime(2025, 9, 1)], y=[5.9]))
fig.update_layout(
 template='simple_white',
 margin={'l': 10, 'r': 10, 't': 0, 'b': 10},
)
fig.write_image(file='t.jpeg')

The result differs between version. Since the tick itself is there, but the label is missing I feel this is a bug. Also margins should not control the plot itself and decide whether or not labels are drawn.