Tx Spectrum variation in AD9364

We are using No-OS driver to configure AD9364 in our project where we are using TxA port for higher frequency and TxB for lower frequency. When we transmit signal with LO frequency of 300MHz in TxA, we are seeing spectrum with increased noise floor and response similar to phase noise roll off. However, when the same signal is transmitted in port TxB, we are seeing a clear spectrum.

Then for further debug, we swap the port configuration such that the TxA will transmit lower frequency and TxB, higher frequency. This time we are facing the clear spectrum(same LO frequency for both port) in both the ports. What might cause the issue? Is this anything to do with software?

I've attached the poor spectrum and good spectrum response below,

.response at TxA port when no swap

Same frequency response in port TxB