Plesk upgrade failed: The installation of the package 'aspnetcore-3.1' failed

Symptoms

• Plesk upgrade failed and this warning appears on the panel

  Upgrade failed. To remove this notice, remove the file C:\Program Files (x86)\Parallels\Plesk/var\upgrade\plesk-upgrade-failure.flag from the server

• The following error was logged to C:\ProgramData\Plesk\Installer\autoinstaller3.log:

  Error: The installation of the package 'aspnetcore-3.1' failed with code 232. (upgrade: Upgrading Microsoft .NET Core 3.1 - Windows Server Hosting...)
  Not all packages were installed.

Cause

Windows updates required to complete the Plesk upgrade are not yet installed.

Resolution

Install all available Windows updates, and reboot the server.

Note: After upgrading Plesk, remove this file to get rid of the warning, if necessary: C:\Program Files (x86)\Parallels\Plesk\var\upgrade\plesk-upgrade-failure.flag