macOS high Sierra 10.13.4 Update restart failed

in my App Store /Updates is displays "macOS high Sierra 10.13.4 Update". The update has been downloaded previously. When I click on the update I get a "restarting your computer" with a count down. When it reached the countdown or the restart button is pressed, I get a notification "Available updates have changed. Click “Show Details” to see the available updates". When I click on the "Show Details", it just goes back to the Update screen. The Mac has been rebooted various time but it does not update the system. The version currently installed is macOS 10.13.3 (17D102). How can I force the update or re-initialize. It's been like this for days.