AP Invoice needs re-validation after the first Approval

Hi All,

Does anyone here know which causes an AP Invoice Validation Status turn to Needs Re-validation after being approved by first Approver.

Please refer to the scenario below:

1. AP Invoice is created, validated and initiated for Approval.

2. AP Invoice will go through a Serial Approval (Approver1 and Approver2)

3. After the Approver1 approved the AP Invoice, the Approver2 cannot proceed to approve.

4. Upon checking the AP Invoice, the validation status changed to 'Needs Revalidation' automatically.

If you happen to know or encounter this kind of situation, please share to us your thoughts or advice on this.

Thank you in advance!