I also have a POD HD500x and and mini mac running High Sierra 10.13.6 on an SSD drive . 8GB RAM.
I updated the drivers via line6 site and POD HD edit still will not recognise the USB connection from 500x - runs in off line mode only even with new drivers. I updated the monkey and edit software as well to be sure. Not recognising my connection. Using line6 supplied USB cable. Most upsetting may give up guitar. NOT!