@ mentions don't trigger a notification for the user that is being mentioned, if you do it after publishing the comment. Like this @nitely
It's intended behaviour. I think my reasoning for not triggering a mention was: if someone edit their comment a month later you would not want to go read an old comment. Or maybe you would?
I think it should be ok to create/update the notification if the comment is newer than the stored one.
I have created a PR. I'll finish it on the weekend