This afternoon we noticed that the position of the B4 beam on the camera 1 had been drifting since a week and was now horizontally miscentered by 1 mm (see Fig.1).
Thus Paolo realigned  the beam at the center of the camera moving in TY the PR filter 7. Fig.2 shows what happened during this realignment. There is a clear increase of power on the B4 photodiode, which confirms that the previous sitation was not good (beam clipping on the photodiode).