Hi, Mike,
There are a couple of baluns and also PI-attenuators connected to the input and output of the ADA4961 on the evaluation board (cf. schematic on p. 23 of the datasheet). The input attenuator has 3 dB loss, and the output one has 10 dB loss, and the two baluns together add another 3 dB of loss, totaling up to 16 dB. So a signal passing through the EVB would see a power gain (from 50 ohm source to 50 ohm load) of 18 - 16 = 2 dB, when the gain of the device is set to its max.
Is this what you observed? If not, please provide more details about device setting, supply current, and signal voltage levels at the input and output pins of the device, so we can make further investigation.
Thanks!
Benjamin