With the ASC IMC model now running at 16384 Hz we look at the coherence of jitter as measured by the IMC WFS and other channels up to 7.4 kHz. Not sure we can conclude anything except that pointing errros contaminate everything.
We can compare this with an older 900-Hz bandwidth measurement from alog 31631 which was taken before the piezo peak fix (alog 31974).
Note that 1084Hz thing doesn't have coherence with IMC WFS.
Can you check the DC sum channels for the IMC WFS as well? They are the ones that hVeto keeps finding as related to the 1080 Hz noise, and they see a modulation in the noise rather than a steady spectrum.
Done, again nothing for the bump in question though there are coherence bumps for f>1100Hz and f<800Hz.