Are you running the 32-bit or 64-bit version of Notepad++?
I am not having the issue you describe. I just copied and pasted a huge document where the word "using" occurs 27 times. If I do an Notepad++ search via CTRL+F, I land on the first occurrence of that word and NVDA announces "Using, selected." Then I close the Find dialog and continue using F3, and on each instance it lands on NVDA says, "Using, selected, unselected." I am not quite sure why that's how it's phrasing it, but I have a guess. The instances are highlighted, much like they are selected, but they're not. I think NVDA's not quite certain initially exactly what is going on, but figures out the correct state pretty quickly. There is about a one second beat between the "Using, selected," and the following announcement, "unselected." I did not keep going enough to make the Notepad++ find function wrap, which it's set to do by default after the last instance of something found has been found and you hit F3 immediately afterward.
Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041
If you think that you can think about a thing, inextricably attached to something else, without thinking of the thing it is attached to, then you have a legal mind.
~ Thomas Reed Powell