Bug or feature on Settings -> System -> Storage?

Hi MaxThunder​,

This is intentional behavior. When Microsoft Defender Antivirus is selected under Settings > System > Storage > Temporary files, Windows removes Defender’s cached data and protection history, including previous scan records. Because that history is deleted, Defender will then report that a quick scan has never been performed until a new scan is run.

This does not affect Defender’s protection or real-time security in any way; only historical logs are removed and they are treated as disposable by the storage cleanup system. While the result can be confusing from a UI perspective, it is currently considered expected behavior rather than a bug. Users who want to keep scan history should leave that option unchecked during cleanup.