I’ve found the “Add From Selection” functionality of the Code Snippets plugin has a tendency to crash Notepad++. It had been reported as an issue but does not appear to have been resolved or assigned yet, unfortunately.
The good news is, there’s a fairly trivial workaround for it in the interim. Instead of using “Add From Selection”, use the Copy command (Ctrl + C on Windows) to copy the selection into the system Clipboard, and then use the “Add From Clipboard” option instead.