When you use the option "Withdrawn from Approval" the workflow is not restarted.
S/4HANA Cloud 2002
When the option "withdrawn from approval is used" in "Manage Purchase Contract" the flag " In Preparation" is activated.
With the flag " in preparation" the workflow will not be restarted.
Once all the relavant changes are set , unflag " in preparation". The contract will be sent to " In approval" as expected.
KBA , MM-FIO-PUR-SQ-CON , Fiori UI for Manage Purchase Contracts , Problem