Might be a known issue. Taking the example from the doc:
select = pn.widgets.Select(name='Select', options={'Biology': 1, 'Chemistry': 2})
If I have have a binding updating the options, the value will update but the UI will take some time to refresh (seems like the whole app refreshes before that to happen).
But if I add a binding on value to take the first value of options as it updates, then the UI refresh instantly.