I was working on a Windows Server 2016 system that I had already configured and put in production. While I was monitoring the resources of the server when I noticed the processes for Windows Defender show up in the task manager as if it were scanning files. This server already had a different AV solution installed.
As it turns out, you need to uninstall Windows Defender feature manually on Windows Server 2016 (https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-antivirus/windows-defender-antivirus-compatibility). Windows Server 2016 will not disable Windows Defender automatically.
"On Windows Server 2016, Windows Defender AV will not enter passive or disabled mode if you have also installed a third-party antivirus product. If you install a third-party antivirus product, you should uninstall Windows Defender AV on Windows Server 2016 to prevent problems caused by having multiple antivirus products installed on a machine."