See https://codepen.io/emmanuelle-plotly/pen/ExVWBdV : there is no transition, but if you remove the uniformtext parameters the transition works again. The corresponding Python code is

df = dict(val=[1, 4, 4, 3], x=['a', 'b', 'a', 'b'], frame=[1, 1, 2, 2])
fig = px.bar(df, x='x', y='val', animation_frame='frame', text='val')
# Comment the line below for transition to work again
fig.update_layout(uniformtext_minsize=20, uniformtext_mode='hide')
fig.update_traces(texttemplate='%{text}', textposition='inside')

fig.show()

This problem was first noticed on the forum https://community.plotly.com/t/bar-chart-animation-transition-breaks-when-uniformtext-in-layout/38394