Due to oscialltions in the X arm IR loop that were causing difficulties in inital alingment, (22443), we made a small change to the Xarm locking filters today (WP#5558).  

There was a pole at 100 Hz that did not make much sense, we moved it to a kHz now, which gives us an extra 40 degrees at the ugf of 100 Hz.  Before and after rms and transfer function screenshots are attached.  This should solve the egregious problem with the 1206 Hz instability, but there are still problems with the loop, which due to the distribution filters in MC2.  These distribution filters are used in MCL, ALS COMM and CARM loops, so we will not try to fix these today.  

First, note that the rms of M2 and M3 are both dominated by things below 0.5 Hz, meaning that we need a boost in the top stage.  We could probably skip M2 altogether as we have done with the recycling mirrors.  Also, Evan and Jeff note that the loop is rather flat around 100 Hz, which is because of a 41z:150p in MC2 M3.