PO workflow sends multiple workitem

Dear Experts,

                   I have created a PO workflow, which triggered on change and releasestepcreated events. This workflow has four level apprval.

It is working fine except, after each approval it sends the multiple workitems to 1st level approver. but there should be not more than one workitem in 1st level when workflow is triggered.

Thanks and Regards,

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Sohail