Hi,
Tax condition record, you can find in FV13 or FV12 t.code.
As already explained - value in NAVS condition type appears from tax procedure with help of tax code. Now check NAVS condition type setting in t.code:M/06 and placement of the NAVS condition type in your pricing procedure in t.code:M/08(also find any routine involved where you have tax amount appear for one vendor but for other vendor not)
Regards,
Biju K