Status in PR (PurchReqTable and PurchReqLine)

I have problem with PR Status using Workflow. Sometimes, when Users already create their RFQ, the Status of the PR in the PurchReqTable and PurchReqLine do not get updated. The Status is supposed change to Pending request for quote when the PR is in the RFQ stage or Pending approval when the PR needs to be approved. Somehow on some PR, the Status does not change from Pending request for quote to Pending approval, vice versa.

Please help me to find solutions. Thanks.