Oracle Fusion Cloud ERP | Issue with Payables Approval Workflow Not Triggering

We are using Oracle Fusion Cloud ERP Financials and encountering an issue where Payables approval workflows are not triggering consistently. Some invoices bypass approval altogether, while others get stuck in a pending state.

We have already validated the following:
• Approval rules and routing configurations in Approvals Management Engine (AME)
• User roles and responsibilities assigned to approvers
• Approval limits and delegation rules
• Transaction criteria used in the approval conditions

Despite this, approvals still behave inconsistently for similar transactions.
Has anyone experienced this in Oracle Fusion Cloud ERP, and what troubleshooting steps or configuration checks resolved it? Please include any AME diagnostics, workflow logs, or setup tasks that should be verified.