It is found, as attached figure 2, that PR and BS mirror had a sudden position change on last Thursday (20210812). This makes the filter cavity alignment totally lost. Since the movement of PR mirror is so large that the PR mirror picomotor needed to be used to recover alignment.

The mirror movement has coincidence with an earthquake (figure 1). But it is the first time I notice that mainly PR pitch mirror is moved. BS is moved a bit as well. But no obvious mirror movement is found for input and end.