Software Update Caught in an Infinite Loop?

I am running a 12" MacBook (2017) with Mac OS 10.13.4 currently installed. The software update function is telling (very reasonably) that an update to 10.13.6 is available. (I don't know what happened to 10.13.5, but perhaps that is another story.) I go to the App Store Update page, and once the .6 is downloaded, the system quite naturally tries to restart, but then a message appears that tells me that "Available updates have changed" and "Click 'show details' to see the available updates." I do so, and that leads me back to the App Store update page where it tells me (again) that I have an update (10.13.6) available for download. So the update function appears to be caught in an infinite loop of confusion. How can I rectify this and cut myself out of the loop?

My thanks in advance,

T. North