I mined it twice in-game but it isn't on the carto map. I've run across a few others as well.
edit: This seems to be fixed. Perhaps it was just a bug with the carto release I was using. Also, while mining the missing node, carto doesn't add it to my map like it used to. Granted, I'd much rather use this database and have a few rogue "missing" veins, I just find it odd behavior.