In version 20.7.5, both debits and credits related to billable expenses are posting to the Billable expenses - invoiced account. Nothing is posted to Billable expenses - cost. As a result, unless there is a markup or discount upon invoicing, the Billable expenses - invoiced account is always zero and Billable expenses - cost is always empty.
This behavior negates a group of changes introduced with v19.11 in December 2019 and makes billable expenses invisible anywhere on the Profit and Loss Statement. It also means Profit and Loss Statements no longer agree with those produced at the end of 2019.