I noticed that the beam centering on the WFS had changed over night and the MC_TRANS_SUM was about 40k counts. When well aligned this SUM is around 50-55k counts. So PSL coupling into MC was suboptimal. It was not clear whether the MC shifted or the PSL beam shifted. So I looked at the PSL ANG and POS QPDs.
The plots above show the gradual drift of the PSL beam in vertical direction during the last 8hrs or so. But the last bit shows the adjustments I had to make to reobtain optimal alignment. And these adjustments are not undoing the drift! This would indicate that the MC axis has also shifted during the same time period.