Try to save as pyCascadingGetApproval flow and change the subject lane in Get Approval via email or that assignment shape calls NotifyAllAssignees to send email. copy NotifyAllAssignees into your ruleset and into your class, and set your subject.
Do you have information how is the out of the box email subject configured? I do not see the email subject line in the the parameters for the notificaitons for NotifyAllAssignees . The subject parameter has "EmailApprovalSubject". I would like to know how the subject line is configured from "EmailApprovalSubject". Please see screenshot.
I can observe that the clipboard Page pyCorrPage.pySubject holds the subject line, but still not sure where it is configured. Updating as looking for a reply.