Besides the unlock due to an earthquake, and the ones intentionally or accidentally caused by someone, a small number of recent unlocks need to be explained. Here is the gps of the events:

1)  1398740055    2024-05-03 02:53:57

2)  1399357405    2024-05-10 06:23:07

3)  1399397637    2024-05-10 17:33:40

4)  1399453603    2024-05-11 09:06:25

5)  1399557370    2024-05-12 13:55:52

The only one for which the Lock Losses Monitor tries to give an explanation is #2: SSFS correction diverging

We see in fig 1 that SSFS Corr was actually increasing because a fast oscillation was growing below the main 150 Hz component. The value was still quite far from the saturation when the ITF unlocked: usually a standard SSFS oscillation can reach 10 V and then cause the unlock. Some disturbance was visible at the same time in some PSL and INJ signals: a correlation is not surprising, but it is not clear to me if the problem was really SSFS or something before SSFS. Experts can better study the data.

The unlocks #1 and #4 come together with a sudden and large fluctuation of the dark fringe (fig 2). A precursor is well visible in BS AA signals (B1p 50MHz QD). The glitches are quite weird: they look like saturations. Before the glitches, the ITF looks quite stable and I cannot find any obvious reason of such a behaviour.

In the unlocks #3 and #5, B1 seems the first to die (fig 3). B1_PD audio channel (fig 4) passes from a normal value to the saturation in 1 ms. Also in this case, the event happens when the ITF looks stable. In fig 5 a normal B1p is visible for 100 s before the unlock. I have checked some other longitudinal and angular error signal, whitout finding anything wrong.