This seems like a known gap, Form refresh settings do not support properties inside a Page List, so your observation is expected. many articles point towards**pyRefreshData** as the supported workaround for non-scalar properties, but it only works when the UI has a dependency that causes the refresh request to fire.
You can try to Create or extend pyRefreshData in the relevant class and place the logic there to clear all values in single page B when the Page List property in A changes. However, if pyRefreshData appears “not working,” the issue is often that the UI is not issuing the refresh call automatically
A practical workaround would be to implement the Page List editing in a modal dialog and clear page B in the modal’s post-processing logic when the user submits. This keeps the clearing logic explicit and avoids forcing refresh evaluation on every field change.
However, if you wanted to still continue with your current implementation of pyRefreshData, then use pyRefreshData plus a field-level visibility dependency so the UI performs the refresh request. Be careful, because this can affect performance if the screen is large.
Do not expect Form refresh to work directly on a Page List property, because it is meant for scalar properties and embedded properties inside a single page, not Page List items.