axis label change via updatemenus not working anymore in 6.0.0

When using fig.update_layout(updatemenus=updatemenus) to change the label of an axis, the axis label just disappears.
Here you find a minimum example that works in 5.24.1 but not anymore in 6.0.0.

import plotly.graph_objects as go
import pandas as pd

data = pd.DataFrame({'x0': (1, 2, 3),
                     'x1': (1, 2, 5),
                     'y0': (5, 6, 8),
                     'y1': (6, 5, 9)})

fig = go.Figure()

fig.add_trace(go.Scatter(x=data['x0'],
                         y=data['y0'],
                         name='0'))

fig.update_xaxes(title='x0')
fig.update_yaxes(title='y0')

bt = []

bt.append(dict(method='update',
               label='0',
               args=list((
                          dict(x=[data['x0']],
                               y=[data['y0']]),
                          dict(xaxis=dict(title='x0'),
                               yaxis=dict(title='y0'))
                         ))))

bt.append(dict(method='update',
               label='1',
               args=list((
                          dict(x=[data['x1']],
                               y=[data['y1']]),
                          dict(xaxis=dict(title='x1'),
                               yaxis=dict(title='y1'))
                         ))))

updatemenus = [{'buttons': bt,
                'showactive': True}]

fig.update_layout(updatemenus=updatemenus)
fig.show(config={'displayModeBar': False})
# fig.write_html('test_5.24.1.html', config={'displayModeBar': False})
fig.write_html('test_6.0.0.html', config={'displayModeBar': False})

To quickly test on the output html files (try the dropdown menu and look at the labels):

• working 5.24.1
• not working 6.0.0

Start with the minimal Python example in the issue and compare the generated test_5.24.1.html and test_6.0.0.html outputs while using the updatemenu. Trace the axis-title update behavior in the relevant Plotly code, then verify that selecting each button preserves the expected x and y labels in the generated HTML.