I am running into a similar issue, where deletion of an item causes this error mentioned in my other reply in the linked thread.
Read-only field is calculated and cannot be set by a client.", field: "order.line_items[10570645].gross_sales_money"
I’m a little nonplussed, as we do not directly touch this field, we only add/remove line_items, and make adjustments to line items (e.g. discounts, taxes)