macOS update installation issue

[OtinG]

Has anyone else encountered this with a recent macOS update?

1. I got the notice in the App Store app that the macOS 10.13.6 update was available to install on my Mac Mini late 2012 running High Sierra. (This happened several weeks ago.)
2. I selected to install the 10.13.6 update using the App Store app Update page. (This also happened several weeks ago.)
3. Installation of the 10.13.6 update seemed to go normally with no noticeable issues and took the typical 45 to 60 minutes to finish.
4. Mac Mini rebooted and restarted normally and when I pulled up About This Mac it verified that the current installed version was macOS High Sierra version 10.13.6.
5. Everything seemed fine, the update ran as expected, no software or OS issues.
6. Within a day though the App Store app was again notifying me that the MacOS 10.13.6.
7. I ignored it and hoped the bogus notification would eventually go away--it didn't. Weeks passed and it was still there

In the past I've occasionally had this issue with app notifications continuously cycling back through the App Store app after being installed, but I had never had this issue with a macOS update.

Yesterday morning I went to wake my Mac Mini but had no luck. Eventually after several minutes it went into update mode and tried to install macOS 10.13.6 again, but the screen eventually froze and nothing happened for over an hour. So I called Apple CS and basically was instructed to unplug the Mac Mini, wait 15 seconds, then replug it in and restart it. It did restart and eventually booted up fine. But the macOS 10.13.6 was still showing as available in the App Store app. I asked the CS rep about that and got no real answer, she basically just sidestepped the issue. I spent over an hour searching the internet and found a lot of articles/threads about macOS 10.13.6 failing to install, but nothing about it refusing to leave the darn App Store app after being installed. I eventually gave up finding a resolution and downloaded the macOS 10.13.6 update directly from Apple server and installed it manually thereby bypassing the App Store app. Installation went well but the darn thing still shows up as needing to be installed in the App Store app. I don't mind the constant red dot on the App Store app icon, but I do mind having to one day again go through my Mac Mini not waking up and restarting causing another hour long delay of use.

Any clues, other than hope for macOS 10.13.6.x update to be released?

ETA: Installing Mojave is really not an option. The older Mac Mini is already sluggish on High Sierra. I wished I had left Sierra on it and never upgraded to High Sierra. But it is basically a backup computer in case my newer MBP goes down, and I mainly use it to run my security cameras for my home and to occasionally run Win 10 via Bootcamp when I need to use a Windows app. It works really well on Win 10 BTW.