Created a software update distribution policy and targeted a group of computers. All but one installed the applicable updates.
Inadvertent Software Update Plug-in policy configurations.
The Default Software Update Plug-in Policy (DSUP) was enabled, and this policy automatically targets any computer with the Software Update Plug-in that is not specifically targeted in an enabled clone of the DSUP.
The clone targeting these systems was disabled, and so the systems followed the DSUPs installation schedule and reboot instructions. However, the Installation schedule start date was set years in the future. The systems that successfully installed the updates were in a different clone of the DSUP that was enabled.
Note: The Windows Systems Assessment scan will only run successfully on computers that are targeted by the DSUP or a clone, if the policy is enabled.