GST Treatment issue

on sales order item table Fields “GST Treatment” with the same set of configuration and Customer, GST Treatment sometimes taken as “Taxable” and sometimes it is taken as “Nil-Rated” due to which it does not Compute GST

If no GST accounts(Accounts specified in GST Settings) are charged in the taxes, the Item is considered as Nil-Rated

Very Thankful to you for your prompt reply
but I have specified the (Account under the GST setting)
@Lakshit_Jain @Smit_Vora please help me with the solution.

Nil-Rated is the default for transaction, if no GST is set in that transaction