I have macOS 10.13.4 on my Mac. In the App Store, it shows 10.13.6 as an available Software Update.
When I click the "Update" button, I get the notification in the top-right corner of my screen:
Restarting Your Computer [Restart] Your computer will restart in 43 seconds [ Later ] to install updates.
When I click "Restart" (or wait for a minute), the App Store window shows a sheet that says:
Available updates have changed. Click "Show Details" to see the available updates. ( Cancel ) ( Show Details )
This aborts the restart. If I click "Cancel", the sheet goes away, and the reboot doesn't happen. If I click "Show Details", the sheet goes away, and the reboot doesn't happen.
If I quit the App Store first and then click "Restart", it opens the App Store again and shows me this sheet.
If I quit the App Store and choose plain "Restart" from the Apple menu, it restarts my Mac, but doesn't install the update.
How do you install the 10.13.6 update on 10.13.4? What am I missing?