HMC7357 failing

I have a design that uses the HMC 7357 with the HMC 980 to control the gate and drain voltage on the HMC 7357 and after a few hours to a few days of operation I am seeing the HMC7357 failing.  The HMC 7357 is operating at 7.7V and the RF drive is 0 dBm.  The amplifier is connected to a 30 dB 5W attenuator.  The RF drive is off when the HMC 7357 is powered up and then once powered the drive is applied.  Before failure the nominal Id ranges from 1270mA before the drive is applied to 1230mA after the drive is applied.  The gate voltage for this configuration is about -0.8V.  After the failure occurs the HMC 7357 gate voltage increases to -0.65V to achieve a 1250mA Id without RF drive and when RF drive is applied the drain current drops to ~800mA and the RF output drops from 31 dBm (before failure) to 10 dBm after failure.  Are there any typical failure modes for the HMC 7357?  We have verified that Vd<9V and Vg>-2.0V at all times while operating and during transients. 

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