> I've seen Windows do that too.

Really? I have never seen this in Windows. Don't get me wrong, I've seen plenty of lock screen failures in Windows, usually in the form of it suddenly being unresponsive, just never anything that actually gave me access to the locked session again.

The closest I've seen is when using RDP, if the Window has been minimized or hidden or otherwise has had reason not to update its display, then locked due to timeout, it will briefly show the last image it rendered when reactivated before updating and showing the lock screen.

P.S.: As other users have pointed out, Windows does have some known lock screen bypasses using accessibility and help dialogs, but in regards to merely crashing the lock screen, I haven't seen it behave in an insecure way.

Yes, really. I don't use Windows myself, but I've seen it happen to others. As another commenter said, it's usually when the computer is coming out of "sleep" or something like that. Plenty of times I've seen a glimpse of the desktop that was long enough for me to get a vague idea of what they were doing before the lock screen takes over. If one was determined enough a photograph could easily be taken in that time.

My guess would be that the video buffer wasn’t cleared before suspending. If so, on resuming there is a race condition between painting the lock screen, and turning on the video hardware that will show the screen memory as it was when suspended.

Huh, interesting. Probably explains why I haven't ever seen it: I never use sleep.

I see this maybe once a week. It only seems to happen when I'm waking the PC.

I've seen this happen on macOS too.

Windows 10 or some ancient version of Windows?

There had been recent bugs on windows 10 where you could navigate your way to a desktop session through the input assistance dialogs (mashing the shift button). They fixed it by removing one of the links in the UI. In older Windows I think it was a mix of help and printer dialogs.