I edited the file manually but apparently I forgot a comma or semicolon somewhere. now my whole file was replaced with the last NPC I added in-game.

I realize this is not a bug, but I would prefer if the plugin didn't load at all while telling me which line/char caused the error so I'd have a chance to fix it without having to re-add all the special NPCs

Always backup any file before editing. and validate any changes https://jsonlint.com/