Abstract:

Sudden lockloss happens at PRFPMI_RF_LOCKED state around 11:52:56 JST.
Just before lockloss, MCL loop has some glitches but I could not identify the glitch source.

Detail:

I kept IFO at PRFPMI_RF_LOCKED state for a while n this morning and sudden lockloss happens.
Figure 1 shows the several IFO signals around the lockloss time (T cursor represents the lockloss time).

DARM, MICH, and PRCL signals seem healthy just before the lockloss.
Transmission and POP90 power seem high enough and stable, so it is unlikely due to the alignment degradation.

Only thing I found before the lockloss is glitches in MNL signals, which is the feedback signals of CARM.
So, CARM loop glitches might be problematic.
Is it a laser frequency glitches?