@Carmak-Cusac said in Npp++ sometimes makes weird line terminations:
Though one reason could it be that I, as I said in my OP, used only \n instead of using \r\n when adding new lines with regex
That is your culprit. To the regex engine, \n means LF character (ASCII 10); that is the definition.
The Notepad++ developers are not likely to hack at a well-established regex engine to make that engine behave differently than it has for all other instances of Notepad++ and every instance of that regex engine throughout the history of the boost regex engine; sorry. It would seriously break most users expectation. The best suggestion I have for you is to learn that in Notepad++ regex, if you want to use the Windows EOL in replacements, you must use the syntax of \r\n, not just \n.