Following investigation. See the attached pictures.

1. What is the reason of the sudden drop of the ITMX temperature? Is it just a matter of sensing circuit or system?
2. There are also drops in the oplev LEN/Tilt sum, which are in principle the same signal, as those beams are originated from the same optical source. So in short, this would mean a drop of oplev sum. If this drop is related with that of ITMX described above, the time delay is about 80 minutes... but if it would be the case, what is the process behind??