Not in any way does this computer issue harm the functionality of your system but it slows down booting and shutting down. The reason for that is the process repeating already installed Cumulative Updates which you are quite aware are among the 'Installed Updates' at the Control Panel.
Image showing Working on updates
When this problem comes up in most case it is as a result of either the operating system did not complete the installation of the Cumulative Updates before shutting down your computer or you have a bug.
The simple means of rectifying the problem is through Disk Cleanup which includes the list of the update files. To do that press Windows Key + R to open Run dialog, type cleanmgr into it and click on OK button to continue. The next thing is to select all the small boxes in the Disk Cleanup dialog and click on 'Clean up system file'. Again select the boxes cleared among those you checked before and click on OK to continue with the process. That will clear up every unimportant Windows Update files that is still remaining in your system. If after that process you are still getting Working-on-update screen when shutting down or starting your system, resort to the following steps below.
Image indicating Windows Key + R in red
STEP 1: Press Windows Key + R to open 'Run' dialog.
Red arrows pointing to process
STEP 2: Type or copy and paste C:\Windows\SoftwareDistribution into 'Run' and click on 'Ok' to continue.
Image showing process in red
STEP 3: Select all the files inside the 'SoftwareDistribution' folder.
Image of red arrows pointing to process
STEP 4: Right-click on the selected files and select 'Delete' from the context menu to delete them.
Image of a system restarting
STEP 5: Close the folder and restart your system for changes to take effect.