Ask the user to perform the same document action using the (slow path). If it works, the issue is isolated to the "Hot Action" customization. If it fails with a different error, you have a standard data consistency issue.

Many organizations implement custom validation in (for POs) or BADI ME_PROCESS_PO_CUST . If custom code contains a syntax error, a division by zero, or a call to a non-existent function, the hot action will abort.

What is the of the document you are trying to process? APP-PO-14160: Document Action Not Completed Successfully