Figure 1. Comparing the spectrum of yesterday to the beginning of the year, the noise level of SRCL, PRCL, MICH is a factor few higher than before. Especially on PRCL. This is also the case of noise on the SSFS quadrature. 

The question is what it is and where it comes from. The noise is likely to be present on the laser frequency, and then polluting all LSC channels. It may be related to the higher noise level of the LNFS.

Figure 2 The more structured noise that is visible in SRCL between 300Hz and 3kHz is very coherent with the excess noise in the LNFS. So that part is clearly due to the more noisy LNFS. For the excess noise in PRCL, and the excess noise in SRCL below 300Hz it is less plausiable. As there is no coherence with the LNFS phase noise, and the LNFS broaband noise below 300Hz is the same as it was at the beginning of the year.

Figure 3 shows yesterday in purple, Friday last week in red, and the beginning of the year in blue. Some version of the pole at 500Hz noise is back, it is clearly visible on SIB2 RFC 8MHz I, the level doesn't appear to be stable as it is different on Friday last week and yesterday, and the changes in noise level of PRCL and SSFS quadrature are correlated with those pole at 500Hz noise changes visible on RFC 8MHz I. 

Figure 4 Looking at data of various nights with arms locked, the pole at 500Hz noise seems to have appeared on October 7. It would be important to look at that more precisely to see at what time the extra noise appeared. One hardware activity on that day was the realignment of the phase camera, and maybe a change in the splitters for the local oscillator of the phase camera https://logbook.virgo-gw.eu/virgo/?r=69877

Figure 5. Searching more precisely it looks like the problem started around 19:00 UTC, there was an interferometer unlock from LN2 at that time.