Since my previous post about this issue I've tried additional measures mentioned in this thread; none have worked. I've been racking my brain trying to find what's different, and why this Scheduled Task works on some setups and not others for no discernable reason. Finally noticed something interesting.
Windows Version:
21H2 -> Scheduled Task OK!
22H2 -> Clean OS install -> Scheduled Task OK!
22H2 -> Upgrade from 21H2, user profile is present before upgrading to 22H2 -> TASK FAILED
22H2 -> Upgrade from 21H2, new user profile created after upgrade and new task created -> Scheduled Task OK!
It appears that something in the 21H2 -> 22H2 upgrade process causes existing profiles to have this trouble.
Creating a NEW user profile and Scheduled Task to "run whether the user is logged on or not" works reliably!
This is not a fix for what looks like a bug in the Windows upgrade process, but it does help narrow down the issue.