I am assuming that swing line is not part of your custom door panel, but created in the door frame object regardless of the door panel used.
If you view the door in 3D and change to wire frame view, is the line there at all.
Maybe hidden inside the door panel thickness?
Versions 6.5 to 22
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision M6800 - i7 4700MQ @ 2.40GHz, 16GB RAM, AMD FirePro M6100 (2GB), Windows 7 64bit