We have lost lock twice in a row after turning up the gain of the soft loops, which seemed to cause an oscillation at around 40 mHz. We confirmed this a few times by tunring them on and off, and watching the oscillation come and go.  We have now turned them on one at a time after increasing the power, and things seem OK.  The attached screenshot shows the POP power fluctations durring the locks over the last 5 days. You can see that as the ground motion became large, the control signals from the soft loops become large and so do the  fluctuations of the POP power.  

CHARD yaw also doesn't seem to have enough juice to suppress the error signal with this kind of ground motion.