On affected devices, Microsoft Defender places thousands of files in the directory: C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store

For example, on a test system running Windows 10, version 20H2, there were more than 10,800 objects in this folder. Other users report that in just 24 hours, Microsoft Defender created over 950,000 files, taking up over 30 gigabytes of disk space. Most files are small: 1 or 2 kilobytes.

The error can affect certain operations, such as sync or backup jobs. [...]