Last night I found that there were many dust particles on the second steering mirror in the REFL path on the AS table.
Looking at it through an IR viewer, I saw the REFL beam hitting one of the biggest dust particles on that mirror.
This dust particle maybe causing the glitches or maybe not.
Anyway because it's always better to have clean mirrors, I will wipe the steering mirror in this evening and check the presence of the glitches again.
The REFL11 and REFL55 demod signals show high frequency noise depending on how big signals go to the POS actuator of PRM.
Is PRM making some fringes with some other optics ??