The agent will check the same items when it starts back up again after a reboot (there are several posts about this on the forum which registry items are looked at) and will keep the “Pending Reboot” state if they aren’t cleared. A single reboot will often not clear out the updates especially if multiples were applied at once so it can take more than one reboot to clear it.
Take a look at Pending Restart...even after Restarting