Normally, macOS updates are a painless experience, assuming that you have what Apple considers a "normal" configuration. Apparently, I fall outside that category.
The only "abnormality" is that I have my Home directory located on an external drive. I do this because I tend to hoard data, and the built-in macOS disk is too small. No biggie, right? Lots of people do this for the very same reason. Wrong!
My "home" user account has "admin" privileges, and with the last macOS update, I launched the update process from my "home" account. (I also have an "Admin" account.). The update progressed normally, without fuss, and after an automatic reboot, I was presented with a login screen. I selected my "home" user account, and to my horror, NOTHING was there. No documents, no Finder customizations, nada. The update actually created a completely new home folder called "billcody" in /Macintosh HD/Users/. My actual home folder is located in /User SSD/billcody.
To my relief, all my data was still on the User SSD drive, but I needed to "re-direct" my "blessed" home folder to this external location.
After plenty of trial and error, here's what I did to fix the issue:
Reboot
Log into Admin account
Delete the "billcody" account just created by the macOS update
Create a new "billcody" account
Log into new "billcody" account, and sign in to iCloud, etc.
Log out of "billcody" account
Log into root account
Using your favorite tool, show hidden files and folders (I use Onyx)
Navigate to /Macintosh HD/Volumes
Witness there is an external volume AND FILE named "User SSD." Delete the User SSD FILE (not the external volume!!!)
Log out of root
Log into Admin account
Go to System Preferences, Users and Groups, unlock, and right-click on Bill Cody account to bring up "Advanced Options..."
Redirect Home folder location to correct folder on external volume (see below). Click OK
Reboot, and log into Bill Cody.
Now, you'll have to re-create keyboard shortcuts, Finder preferences, etc., etc. In all, a ton of unnecessary work.
SO HOW DO I AVOID THIS MESS?
Easy. NEVER ever perform a system update from a "user" account, regardless of privileges. ALWAYS perform system updates from your Admin account. I did it this way on my second Mac, and the update went flawlessly. Additionally, I changed my access from Admin to Standard on my normal user account to act as a deterrent should I forget my lesson.
Consider yourself warned.