personally, it is easier to read in rows. Lang xing is far away, so it is necessary to "chase" from the soul. If it is Lang hang, where is the word "chase"? However, when wang hong, a teacher from Sichuan University, taught the course of China's poetry art in MOOC, he specially emphasized that "line" here should be read hang, which means "over there". Never pronounce it xing. I didn't understand at the time.
I saw the explanation of this poem in the ancient poetry network: "Langxing" means "Langbian". At that time, it was said that she even left her body and chased the poet to a distant place.
for reference.