I ran into this issue the other day, sort of. I was on Atlantic picking up a purchase I made. While there I figured I'd buy some items I can't normally find on my home server. Shadowguard drops and other rare drop items.
I literally searched for an item and found it using my search term. However, as I was scrolling through the list of items, as it returned many matches at different prices, it errored out. When I searched for the same exact search term again I kept getting that too vague error. I tried restarting my client, my computer.. same thing. I think it's a bug and I haven't figured out how to get around it.