Looks like the marked state line (confirmed by the Polk County welcome sign) crosses the northern corner of the Toccoa Ave./ Harpertown Rd. intersection, which is where GA 5 makes a turn and also GA 60 begins. Would not over-simplify things to just move the south end of tn.tn068 to that intersection, and get rid of the ga.tn068 route file.
Aside from the pavement markings and the state line signs on both sides of that intersection, some but not all of the online maps in the Waypoint Editor have the state line cutting through the intersection.
This is yet another reminder that online maps (especially Google Maps, which I've found to be a major offender) often misplace borders, and signage can be more accurate.
Good catch!