The top string is tough on any guitar. I agree that it is highly unlikely related to the luthier's instruments.
Try the nut, you can put a piece of cardboard around the string at the nut (hold a piece of a business card in there while you tighten it back up, then trim. Is it better? If so, its the nut. If not, try other strings. I have had issues like this, try Savarez New Cristal and D'Addario Pro Arte EXTRA hard tension, they are both warm nylon strings, more so than the Augustine.