As I reported in klog34027, SR2 yaw motion is currently very large.
To evaluate the effect of SR2 angular fluctuation, I checked the spectrum and coherence of SR2 OpLev and AS_17Q error signals (fig1).

AS RF17 Q signals have a peak at 0.188Hz, which is the same frequency of the peak in SR2 yaw.
In addition, AS RF17 Q signals and SR2 TM yaw signals have a coherence at the peak.
Since AS RF17 Q signals are monitored DARM fluctuation well at low frequency, current SR2 motion seems to coupled to DARM thorugh misalignment to OMC.

This results in the optical gain variation in time, so it should be fixed for stabilizing IFO control and sensitivity.