Initially I thought this moth to be incapacitated. It still moved, but seemed unable to take off.
I photographed it at around 9 a.m. At around 12 a.m. it was still at the same spot, so I got an insect box, came back and caught it.
I donated the individual to Entomologist Dr. Lee Kang Woon, head of Holoce Ecological Academy. He has a breeding program of Langia zenzeroides. Dr. Lee identified this individual as female, and said that the species in Korea is limited to Kangwondo, and that he pushes for it to be recognized as an endangered species.
L. zenzeroides feeds on Prunus sp. At Holoce these insects are kept in cages lying on the ground, the bottom of the cage covered with leaf litter. L. zenzeroides spends much of its time in leaf litter, where it is well-camouflaged. This explains the behaviour I earlier misinterpretated as incapacitated : these insects move mainly by walking/climbing, and they seem to use their wings for getting into the trees to feed.
Reference : Caterpillars of Moths in Korean Peninsula vol.II pp.142-143 by Dr. Lee Kang Woon