Please tell what is the output power of AD9371 IC in bist mode?
Looks like the matching is not correct. You can use the S parameters models available as part of the design file package and then simulate with it and check if you are getting a good return loss or not.
Check the power supply, if you are getting a bias current of 100mA on each differential line. At full output power, each differential output side draws approximately 100 mA of dc bias current.also, check for the voltage drop(ΔV across the parasitic element) if its correct.