zdnet[.]com/article/windows-defender-malware-scans-are-failing-after-a-few-seconds/
Microsoft tried to fix another bug, and created this one.
Running a Quick or Full scan will fail after a few seconds and only go through a handful of files, resulting in incomplete, superficial results. Such scans are usually known to take tens of minutes, and even hours.
In an email to ZDNet, Microsoft confirmed the bug and said the company was working on a fix. The company said that only manual or scheduled scans were impacted, and that Windows Defender's real-time scanning protection was not impacted, and should detect malware once it reaches a system.
Instead of relying on a Quick or Full scan, users can use the Windows Defender "Custom scan" feature and select the drives or folders they'd like scanned, manually, one by one.