I don’t know if you have figured this out by yourself yet, but it appears that Notepad ++ breaks several file associations (at least on my systems) that I have had to manually fix - .bat, .cmd, .ini, .inf, nfo. and .vbs. The easiest way to fix this is via the ASSOC command from the (Administrator) command prompt. The best way to check which associations need to be looked at is to run ‘assoc’ and copy-and-paste the results into (ironically) Notepad ++ and look at which ones are associated with NPP. You can get the syntax by typing ‘assoc /?’ at a prompt. The proper associations for the ones listed are:
.bat=batfile;
.cmd=cmdfile;
.inf=inffile;
.ini=inifile;
.nfo=MSInfoFile
.vbs=VBSFile
It also seems to grab .bash file extensions too, but unless you have the new Bash shell on Windows 10 installed this won’t matter.
Hope this helps!