HI Abhishek,
THere can be 3 reasons:
1. NPV is not set to zero at the inception for the derivative(based on hedge stratefy selected) . You can do so by running THM30.
2. The inception date of the Hedging Relationship and the effective start date of the swap do not correspond to each other.
3. The exposure amount is with opposite direction as compared to the swap.
Regards,
NIkhil