With 1902 CE we have provided additional features in the workflow restart of Purchase Requisitions :
Critical changes made to the existing purchase requisitions will re-trigger the workflow. The following configurations are available to determine what shouldn't retrigger the workflow:
- To maintain the fields for which restart of workflow is applicable, use the configuration step Manage Conditions to Restart Flexible Workflow in Manage Your solutions app.
- To decide which critical changes lead to restart, you can create an implementation in Define Conditions to Restart Flexible Workflow in the Custom Fields and Logic app. For more information go to help.sap.com SAP S/4HANA Cloud General Functions for the Key User Extensibility Custom Fields and Logic.
See also this KBA with examples :