Issue with Invoice Approval

Summary

Invoice not captured by Initiate Invoice Approval Workflow

Content

Hi,

We found a validated invoice which is not captured by the Initiate Invoice Approval Workflow job, so the approval process does not automatically start. We have this process scheduled 4 times per day, for each BU. This Invoice is not captured and remains with Approval status "Required". Further, with sql, we have identified a few other invoices with the same issue, we have not found a link however. 

Do you have any suggestion as to why this might happen?

Thanks & Regards,

Tudor