Wrong Item Category Determination in Sales Order

Dear Experts,

We are facing a strange issue where wrong item category is getting determined in some of the Sales Orders at production instance.

Actually under our scenario Sales Orders are created through CRM IC portal which are finally posted to R/3 system which we can view under VA03 transaction.These sales orders carry Non Stock Items for which the item category should be determined as the "Item Category for Non Stock Items" under Sales order but for some of the cases its getting determined as TAN instead of e.g. ZNSX. Hence availability check is getting conducted at the Sales Order as a result items are not getting confirmed in Sales order for Non Stock Items.

We have checked all the configuration set up, change logs and observed nothing is changed so far.

This issue is very sporadic in nature and even on production system its not getting replicated again at both of the systems (CRM & R/3).

Since the issue is really hampering our business transactions now we want to fix this issue at the R/3 side.

Whether any body has faced such kind of issues ?

Kindly advise what fix we could apply at the standard program to resolve this issue.

Thank you,