The first attachment shows how H1's range has degraded over the last week, with the first incident of poor range happening before we started to move PR3.

It seems that there are mulitple issues.  The squeezer seems to be intermittently adding low frequency noise, see 77969 and 77888.  This morning I repeated the squeezer on / off test and see that the low frequency noise is worse than May 8th now but isn't from the squeezer.  The low frequency noise could be explained by the PRCL coherence, which is higher than either SRCL or MICH coherence.   (Similar to what Camilla saw last night 77976). 

Looking at the trend of the range with PR3 alignment, it does seem that the nonstationarity is present when we have PR3 moved, and mostly gone when it is in the original position.  There was one incident of low range right before the move, which seemed related to anthropogenic ground motion.  The range dips at times when PR3 is moved do not seem related to the ground motion. 

This morning I made an attempt to move the squeezer alignment to see if this would help with the low frequency noise.  I put a length excitation on ZM5, and increased the amplitude until I saw fringe wrapping in DARM.  This template is saved in useraps/sqz/h1/Templates/dtt/DARM_scatter_bad.xml  I moved ZM5 - 47urad in yaw, and saw that this reduced the amplitude of the scatter shelf (screenshot).  Once I ran the SCAN_ALIGNMENT script which adjusted ZM4+6 to reoptimize the squeezing, the shelf height was mostly back to it's original.  I've left the squeezer in this new alignment, but I'm not sure it's worth pursuing this until a time when the intermittent squeezer problem is happening.