Windows 10: Windows Defender not completing scans other than quick scan

Windows defender will not complete any scan other than a quick scan. This problem has been occuring for a few months. Windows Defender is the only antivirus installed on my computer, so it is not due to a compatibility issue. I have checked for updates, both for Windows and Defender itself, and there are none. I have tried using sfc, which did mot detect any issues. I tried deleting the scan history as was recommended in anohter post on a similar issue, but was not able to due to not being a privilidged enough user, despite being admin. Any advice would be appreciated

:)

 

Windows Defender - Quick Scan

Windows defender no longer offers a quick scan option.

My options are:

• Scan
• Advanced Scan

• Full Scan
• Custom Scan
• Windows Defender Offline scan

Whichever option I check, the scan will need to run for hours to complete.

Is a quick scan available?

How do I restore this feature?

 

Windows Defender quick scan fails to complete

When I try to employ a "Quick Scan" procedure in Defender, the scan progress indicator, coloured green, stops half way and does not complete.

The files scanned number continues the count as if it is doing a full scan.

My Windows 10 updates are correct as our the virus definitions etc.

Any suggestions on why the "quick" scan fails to complete?

Thanks

[Original title: Windows 10 Defender]

 

Does Windows Defender Quick scan interrupt Advanced scan?

Before I create a System Image, I run an Advanced scan using Windows Defender, and it typically takes about an hour and the Scan history lists about 4,000,000 files scanned. However, often I see only about 40,000 files scanned, what I get from a Quick scan.

I can think of two explanations that might account for this:

1. The Advanced scan completes, but a Quick scan starts afterwards and wipes out evidence that that the Advanced scan occurred (unless presumably some problem was found).

2. The Advanced scan is interrupted and a Quick scan runs.

Are there other possibilities?

The 2 possibilities listed above are both unsatisfactory because I can tell if an Advanced scan was completed. If an Advanced scan was just completed, there is no reason that a Quick scan should be run automatically.