If you are using assign_async for a specific assigns key, you must keep using assign_async. Otherwise, you will get error like this:
(phoenix_live_view 0.20.9) lib/phoenix_component.ex:3027: Phoenix.Component."async_result (overridable 1)"(%{loading: [%{inner_block: #Function<28.40661718/2 in
So if you start with assign_async in mount, you need to use assign_async in all other event handlers.