Elias here with Shopify Support. Thank you for reaching out.
I understand that you’re trying to update the cart and you’re running into an error removing the product, as the product has already been deleted from the backend. I think the browser might also be caching some of the data from the store, so clearing the browser’s cookies and caches may help resolve the issue. With said said, have you tried clearing your browser’s data already?
If not, please give that a try, and if the issue persists - Simply get back to me here and I’d be happy to take a closer look.