I'm thinking Windows 11 downloaded updates/patches about the same time I installed Bitcoin Core v25.
In a pinch, I can use a separate Windows 10 server for Armory, but that's an old PC I'd like to use it for other purposes.
Windows 11 is my fastest PC, so if I can figure out this problem, it would be awesome.
If you think it's the cause of the issue, then try to uninstall the latest updates of your W11 machine.
Refer to this article to see how:
support.microsoft.com/en-us/windows/how-to-uninstall-a-windows-updateThen, since you've already downgraded and confirmed that you have the complete blockchain but the issue remains, then we can deduct Bitcoin Core out of the suspects.