BigQuery non-incremental materialized view is not refreshing as expected. How does it refer to the base table?

Question

I am creating a materialized view with a ROW_NUMBER() function in my query. Since it's an analytical query and incremental materialized views do not support those functions, I'm creating a non-incremental view with 30 mins refresh interval and 1 hour staleness limit.

My query looks something like:

CREATE MATERIALIZED VIEW `project.dataset.mat_vw` 

AS SELECT * FROM (
  SELECT * FROM (
    SELECT * FROM `project.dataset.BASE_TABLE`
  ) WHERE xyz
) WHERE abc

In the project history I can see that bigquery admin refreshes the mat view, but the mat vw doesn't reflect the changes made to base table before the refresh on mat_vw is called.

In this case, since there are derived tables between the base table and materlized view,

• What is the base table?
• Why is it not picking up changes from BASE_TABLE?
• Do refreshes happen every 30 mins as configured, or is it in someway dependent on base table?
• How does the data staleness option work? What is it based on?