I've got two Win10-64 boxes running 'Feature update to Windows 10, version 1709 and the latest KB4056892 2018-01 cumulative update for windows 10 version 1709 x64-based systems.

With one box, I can right click on the latest firefox 64 bit exe installer and can 'scan with windows defender' and it will scan 598 files. On the other, the scan of the same file shows '1 files scanned'?

I just can't figure this out? How can I resolve this? It makes me question whether Windows defender is working at all?