Need return value only if document is updated else ignore

SQL++
2

Returning clause returns qualified mutations as you don’t have any predicate every document qualifies update (in set clause you updating some cases same document with same value).

UPDATE default 
SET Bookings = ARRAY book FOR book IN Bookings WHEN  book.EndDate > "2017-07-19" END
WHERE ANY book IN Bookings  SATISFIES book.EndDate <= "2017-07-19" END
 RETURNING Name;

If you want query run faster create following index

CREATE INDEX ix1 ON default( DISTINCT ARRAY book.EndDate FOR book IN Bookings END);