According to a BornCity post, the issue was addressed in a March 24 update. The update that you need to install to resolve this issue is KB4052623, which is described as an update for the Windows Defender AntiMalware platform. Can be installed on operating systems Windows 10, Windows Server 2016 and Windows Server 2019.
The strange thing is that the official KB page states that the latest version of KB4052623 released on March 5, while on the other hand, the Microsoft Product Update reports that a new version was released on March 24th. In the Microsoft Update Catalog is not referred to as an update to the antimalware engine, but as "definition updates".
However, the Microsoft confirms that after installing this update on March 24, the Windows Defender build will be released in version 4.18.2003.8.
The problem occurred because Windows Defender could not scan network files and Microsoft states on the KB page that it is aware of a problem that is causing high network traffic.
"Companies that use Network Protection either in control mode or in block mode may experience higher network traffic than expected in domains that use their SmartScreen Microsoft Defender. This affects customers running version 4.18.2001.10. We are working on an update that addresses this issue. "In the meantime, you can resolve this by temporarily disabling Network Protection." Microsoft.
You can update the Windows Defender antimalware engine from: Windows Security - Antivirus & Threat Protection - Antivirus & Threat Updates - Check for updates.
You do not need to restart your system after installing the update.