Windows 10 Pro shows background, but no login form

Windows 10 Pro shows background, but no login form

Occasionally, some folks at my workplace have had a problem where after awakening their Windows 10 Pro PCs and laptops, just the background of the login screen shows, but there are no text, fields, or buttons.

Although there are no instructions on the screen to do so, pressing Ctrl-Alt-Delete reveals the normal login screen.