I called ebay Application Support team, she was very helpful and said the error is hard to figure out on their end. It could mean anything from server down to application conflicts. She suggested other ways to bulk list (File Exchange, Turbo Lister and the new Ebay Seller Hub) but they ALL have one thing or another wrong with the applications and doesn’t support everything GS does.
I bit the bullet and ended up upgrading to High Sierra. It was Sierra (not High) that was giving us all the problems with bugs so I guess High Sierra is fine now. I had to upgrade to GS7 to get everything working again. I lost 3 applications due to non compatible with High Sierra (exactly what I was afraid of) now I have to get those programs again.