Try running the Client Side Script on an affected computer. If it helps, do this on all of the others. If it doesn't, please continue down the list.
https://www.ajtek.ca/wsus/client-machines-not-reporting-to-wsus-properly/
Also, are the files downloaded properly to the WSUS server? What does the file status column show? You might need to add the File Status column to your view.
https://www.ajtek.ca/wsus/how-to-setup-manage-and-maintain-wsus-part-2-computer-groups-update-views/