I gave a further look to the unlocks of Jan 7th, in particular to the once happening before LN3, which are slower and allow to appreciate the high order mode rising up on B1p camera.

The shape of the high order mode appearing right before the unlock evolves in time, passing from an HG01 on Jan 7th to an HG10 on Jan 8th (see figures 1 to 3). This latter is visible only in the last unlock before the normal operation of the interferometer is recovered.

Comparing the frequencies of the 155kHz line in the first and last case, they differ by almost 1Hz (figure 4). The temperature variation of the NI test mass is about 0.1K (figure 5), which would give a frequency shift of ≈1.7Hz, so it's difficult to understand if the line which gives rise to the two event is the same and is shifted by the temperature or maybe it's another mode which gets excited. 

Looking at the B7 and B8 signals sampled at 400MHz, it seems that on the event of Jan 8th a small peak at around 150kHz is also visible on B7, but it could also be some random noise. Still to understand why no clear signal is visible on B7.