User is trying to create an invoice from a project's Billing Schedule using the More > Create Invoice option, but the markup on the expenses decreases on creating that invoice.
This can happen if the total amount from the approved billable non-extra expenses that you are billing on the project is more than the Net Bill amount that you have set for the Billing Schedule. BQE CORE adjusts the charge amounts for the expense entries by changing the markup. Check CORE Help Center for details.