Oh yeah, just to note:
Neither setting NVDA back to its defaults, nor even completely reinstalling it solves the issue, we did both, reinstalled it when changing from Windows 8.1 to 10, and did reset it to defaults a few times after it...nope, the problem still keeps occuring.

It's a desktop, as a devoted and passionate gamer, I never used laptops in my life.

And I have no idea what Jaws has got to do with this...I use NVDA, always used it since my vision loss, we did intend to try out Jaws too, so a misfunctioning copy of Jaws was installed, and then uninstalled from my computer, but it was under my previous system, Windows 8.1, my hard-drive, (actually system drive C),  got cleared, and windows 10 installed to it over a year ago, normally with the only one, NVDA screen-reader this time.

let me ask why I asked about JAWS. JAWS has a setting, where it can modify the start of the numlock key. so what I was thinking of, if the PC goes to sleep, and you used JAWS on the log in screen, maybe that had to do with it. since you don't have JAWS, I don't have any ideas at the moment.

NVDA doesn't do that. The guys there realize its your computer and you'll set it up how you'd like, they don't mess with it XD. On a more serious note, it does sound like maybe you accidentally remapped a key somehow, I don't know dude, this just sounds odd, like really odd. In the Track Kings topic, you said you were fluent in German, does that mean you have the German keyboard layout, if so, I'd switch to it and hit the key that's the backslash in your layout, if it doesn't trigger, hit the German backslash key and see if that triggers, its not really an end solution per se, but its a path to potential clues, and I think we could use some more clues to help solve this, because I honestly don't know at this point.

No, not really, but I was thinking more along the lines that something happened with your character map, so switching keyboard layouts to see if a different language's keymap stops this behavior was one troubleshooting step that might have yielded a clue as to the root cause.

Oh, and just to clarify something, what may be of a great importance:
(foolishly I forgot to mention it before)

I don't know where the / symbol is on other keyboards, I even forgot where it was located on the english one, (which I have used for many years back in Yugoslavia), but on hungarian it is right next to the num-lock key, so the next, adjacent key to its right.
Normally, being there is also the reason of its secondary, left-mouse-click function in NVDA, which activates each time num-lock is turned off.
(and causes my problems each single time)

Of course, there is supposed to be a 2nd alternative for the / symbol somewhere, but it's probably working with certain key-combination, using which, since typing blind, would also be a slower, and less comfortable solution.

post 13 confused me. isn't numlock to the right of backspace? that is, if a PC has a number pad at the side. I have UK layout, with computers that were manufacturered for UK use, so my keyboard layout may be different, but yeah, that got me wonder. computers without a number pad, simply don't have a numLock by default, unless there is a hidden key somewhere. while interestingly, my mother language is also hungarian, everything on this end is 100% english. suppose I could pull out the keyboard and give it a good old play if that helped, but well.

Woww, over 3 days have passed, and still no issue...is it possible what I did still fixed it?
Is HK keyboard-configuration set the same way by you guys too?
(meaning the other NVDA users of course)