OKAY... TWO POINTS AFFECTING SCREENSHOTS!
#1, Your AV Ransomware can stop the save. I have Avast Premium (about to let it lapse) that even though I put in an exception, still blocks the shots. I even tried making an exception for the screenshot folder. No Go... But the instant I turned off Ransomware Protection the screenshot appeared... but only the last one. That affects BOTH F10 and ALT-F10 shots.
#2, For Nvidia users... the Geforce Experience IF you've installed it) has a Default keybind to ALT-F10 for something. (I forget). You MUST change the keybinds for G.E. or it will keep you from making High Rez shots too. Just go into Geforce Experience and change the keybinds.. OR, Just delete the Geforce Experience. I find that the G.E. software NEVER gets the Auto-Graphics "Enhancement" right, for anything! Why even have it?
So.. ANTIVIRUS and GEFORCE EXPERIENCE can BOTH prevent screenshots.
Good Luck... took some deep diving several months ago to get this one down.