SalesInvoiceLinesBulk, discount (no line, but total discount on the invoice) is missing.
It is no line (but a total discount on the invoice), therefor it is missing, if possible / on the agenda maybe easy to apply in the export.
You might want to check the table SalesInvoiceLinesIncremental. It has a line number 0 for the header (see Special line number such as 0 and 9999 on financial transactions in Exact Online). Maybe that one reflects the invoice discount.
An alternative is to check the contents of the table ExactOnlineREST..SalesInvoices.