Invoice spreadsheet approval assigned to approvers in parallel instead of serial

Hi,
Customer has defined the Payables Invoice Workflow rules using the spreadsheet in the same block. When we submit an invoice for the IND BU, the workflow is being triggered as expected and is routing to job-level hierarchy approvers serially.

*Rule Description	*Approval Routing	Business Unit Name
US_Rule	Group in Serial	US BU
IND_Rule	Job Level Hierarchy	IND BU

Customer recently changed the US_Rule (Approval Routing) from “Group in Serial” to “Group First Responder,” and no changes were made to the IND_Rule.
After this update, when we submit an invoice for approval under the IND BU, the workflow is pulling the correct job-level approvers. However, the notifications are now being sent in parallel instead of serial, and if any one approver takes action, the approval status is immediately updated to Workflow Approved.