Complex sentence: Problems with tight coupling can arise with the "freshness" of data; for example, when an original data source gets updated, but the warehouse still contains the older data and the ETL process needs re-execution.
Split into simpler sentences: Problems with tight coupling can arise with the "freshness" of data, which means information in warehouse is not always up-to-date. Therefore, when an original data source gets updated, but the warehouse still contains the older data and the ETL process needs re-execution.