The system might be affect by strong EMI.
Depending on the test of 120MHz 1dBm, AD8605 output is wrong.
Of course the customer takes case about pattern layout. they put 1Mohm resistor near the pin.
But the issue is not cleared.
Can the customer put bypass capacitor?
This would be silly question.
Is AD8603 stronger than AD8605 about immunity?
It is helpful if there is critical solution about it.
There are many ways to filter out EMI. You may want to implement the circuits on pages 5 and 6 (to eliminate EMI at the inputs) and pages 8 and 9 (for the outputs) of this article - http://www.analog.com/media/en/training-seminars/tutorials/MT-096.pdf
We cannot tell if AD8603 is stronger than AD8605 in terms of immunity unless we test it. You may consult the Reference 1 of the article above for the RFI test.