I have done some testing and found the behaviour that you have mentioned. While it can work with Invoice Id mentioned, it does not when one or multiple invoices are settled using checkbox, on the new pop-up form that is opened from the Settle Transaction Button.
This would need customization by adding a new method in the class named as LedgerJournalWFApprovalDocument
The newly added method would be on the same pattern as an existing method in the class (parmMaxVoucherCreditAmount)
Once a new method is added using extension, that would make a new selection possible in the workflow conditions.
If you have a technical consultant, tell them following.
1) initially when a transaction is marked it remains in a table named SpecTrans (until payment journal is not posted). The table maintains the record using three key fields RefCompany, RefRecId, RefTableId
2) Once payment journal is posted the records go to the table VendSettlement and get deleted from SpecTrans
3) therefore your custom method must check both tables, for marked transactions.
In technical language it is called adding Calculated Fields in the workflow document class, that enables a new selection on the conditions of workflow
You will get a new choice on the following form:
