What is the root caus of the the hold "Maximum Schedule Amount"?

Summary

We have several invoices with the hold "Maximum Schedule Amount" but when we review the associated PO, the invoice matches. What is causing this hold?

Content

We have a number of B2B xml invoices that were imported and are on hold with the Hold Name "Maximum Schedule Amount" and Reason = Variance between invoice and schedule amount exceeds limit.  The Held By is the person that imported the invoices.  Typically Purchasing Holds are shown as Held By the System, not the user.

When we review the associated PO the Schedule matched the invoice.

We are trying to determine what would have caused this hold to be placed on the invoice.  We are working on releasing the holds manually in order to process the invoices, but would like to know more about what might have caused them.