Incomple Status for POs

Experts,

We have our process configured such as once the req is approved, POs should be approved automatically however there's an scenario where this is not happening.

We realized that when user manually change the tax code while submitting the requisition for most of cases, the field TAX ATTRIBUTE UPDATE_CODE got UPDATE value, and the PO is created but Incomplete.

There's specific tax name where it does not apply an PO got completed

I'm looking first, how can I track the path the workflow followed in an incomplete po if there's not workflow assigned.

and second, can we know if there's some kind of relation between the location and the tax code,  locations have a tax code assigned in the "other details" tab but when this tax name is changed while submiitng the requisition for most of them, pos got incomplete status.