As part of a different investigation (still trying to understand why our range goes bad sometimes), I incidentally may have found a source for some glitches / range drops. 

I'm not going to look further into this, but instead tag detchar-request in hopes that someone else has some time to think about it.  I'll also directly send messages to Jim and Elenna, who manage this feedforward system.

In the attached screenshot there are a few channels that include 'TTL4C' - those are the tabletop L4C seismic sensors on HAM1.  There are also 'FFHAM1' channels that take a channel derived from those L4Cs, and feed it forward to the error signal of the ASC loop that is referred to in the name.  A moment or so after there is a glitch in those channels, there is a range drop in DARM. 

I will say that when I zoom in, it looks like the glitch appears in the FFHAM1 channel before it appears in the TTL4C channel, but based on my understanding of the signal flow, I'm not entirely sure how that's possible.  I'm hoping that Elenna (who knows much more than I do) can help think this through.