Slow crash resulting in being unable to open programs / full restart required

[PrinceBrightstar]

I've experienced a system crashing issue since the rollout of patch 6.4. I've been ruling out pieces of software and I'm down to it being FFXIV and some other software that seem unlikely to be the cause as they don't receive updates.

Basically once the game is booted up, at some point in the future (Sometimes days in the future) my system will lock up in such a way that it will not open any new programs when commanded, and if I go to lock the computer, it will result in either a black screen requiring a hard reset, or I will get the following error, also requiring a hard reset.

"Failure to display security and shut down options // The sign-in process couldn't display security and sign-in options when Ctrl+Alt+Delete was pressed. If Windows doesn't respond, press Esc, or use the power switch to restart."

Obviously Windows Logon/Security being tampered with is a very serious issue.
I've already attempted using the sfc /scannow and DISM commands so there's nothing wrong with the Windows Image. I've also tried a full reinstall of FFXIV to no effect.

I'm mid "crash" right now as I write this unable to open an app like PowerPoint after closing the game a few moments ago. I also opened an instance of Chrome about 15 minutes prior to closing the game without any issues. Sadly trying to get the System Information from the game launcher isn't possible since even that won't load and just shows the Final Fantasy XIV logo. I'll get that data after the next restart. Not even my task manager will display any programs under the Details tab for me to try to close that out. Not even going to start - shut down - restart works. I have to hit the hard reset button on my case when this happens.