Why IEX: Strategy Fulfilment Mailer not pickup data to generate dunning letter automatically even we

Why does the Workflow background process "IEX: Strategy Fulfilment Mailer" not pickup data to generate dunning letter automatically even we schedule this job to run periodically?

• No issue when I do send individually by click the Send Dunning Letter button
• Correspondence templates have been assigned to Workitems.

Release: 12.1.3

Profiles:

• "IEX: Deliver Dunning Letters" Set to Immediate
• "IEX: Process Strategies by Operating Unit" is set to 'Operating Unit' at site level

Set Up Summary:

• Collections Correspondence Delivery Method XML Y
• Dunning Plan Aging Bucket EXP 7-Bucket Aging Y
• Collections Dunning Level BILL_TO Y
• Collections Strategy Level BILL_TO Y