Yesterday, when we locked the cavity, we had to set the local control of the pitch of the end mirror at -4.8 (on a scale from 5 to -5).
Today, it was not possible to lock the cavity because of a drift of the end mirror.
When we went to the end room to reset the local control, the temperature and humidity of the end room was quite high.
It appears that a air ventilation system was off. As soon as we turned it on, it started to feel more confortable.
After resetting the end mirror local control, it was possible to lock the cavity again.