Windows Server 2016 is not showing cumulative patches past 2018-05
Issue
Windows Server 2016 no longer displays any cumulative patches past 2018-05.
Cause
The device has 2018-05 Cumulative Update for Windows Server 2016 for x64-based Systems (KB4103720) installed, but not 2018-05 Update for Windows Server 2016 for x64-based Systems (KB4132216).
Resolution
Install the Windows Update 2018-05 Update for Windows Server 2016 for x64-based Systems (KB4132216). As per Microsoft's release notes, this update "addresses an issue that might sometimes lead to incorrect checks for applicability during installation of Windows Updates".