Michal pointed out that last Sunday (Dec 17) there was mistuning of the relative curvature of the north and west arm: https://logbook.virgo-gw.eu/virgo/?r=62766.
Due to this between 15:00 and 18:00 UTC the B1p power was higher by about a factor 2, and many lines became much higher in DARM (Figure 1).
These lines might be related to some mechanical resonances on the detection side (if it is scattered light related) or to the injection side (if it is frequency noise related).

Most of the peaks had indeed been already observed, as reported in https://logbook.virgo-gw.eu/virgo/?r=62730, many peaks have also been excited with environmental actions (tappings: https://logbook.virgo-gw.eu/virgo/?r=61929 , https://logbook.virgo-gw.eu/virgo/?r=62172  and https://logbook.virgo-gw.eu/virgo/?r=62759).

The fact that peaks are excited with tappings on the vacuum chambers and moreover that some are coherent with accelerometers attached to the chamber, suggests that these peaks are mechanical modes of the chamber itself or of objects attached to the chamber (like e.g. baffles) which happen to back scatter some light.

This table lists all these peaks and summarizes some info. See also this table: https://logbook.virgo-gw.eu/virgo/uploads/62172_1697216708_tabella_tappings.png

Attached figures 2 to 4 show the observed coherence.