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.
2017 Glenn Canin Spruce