Some orders has the array "marketplace Items" filled with more items then the array "items" of json order. This setup is normal and is regarding for example "wedding gift list". But the New UI is not prepared to handle these kind of orders with items on "marketplace Items" and broke the page with an error message:

"Sorry, something went wrong on our side. Please try again or refresh the page. Back to the list"

Create an order with catalog using array "marketplace Items", after that you can try see the order on UI admin. The UI will broke and show a message error.

Use the old UI to open that order.