When combining VSI's which has same Operation names but different signatures, seen the transactions are added to Specific Transactions instead of adding it to Stateless Transactions.
Steps to reproduce:
1. Create a Main.vsi with the below Stateless Transactions:
2. Then create another New.vsi with the below Stateless Transaction.
The  Stateless Transaction -->META Transaction has Operation as Match Style which caused the issue.
Release : 10.x
Component : CA Service Virtualization
Here are the steps to resolve:
. In Main.vsi, change the  Stateless Transaction -->META Transaction--> Match Style from Operation to Signature.
. Delete the added Specific Transaction from the Main.vsi and save it..
. Close the Main.vsi and New.vsi files.
. Retry combining New.vsi into Main.vsi.
. Open the Main.vsi and should see the new transaction in the Stateless Transactions list as in below screenshot.