When the Operator found the ISIs in the wrong SDF state, 21609, they reported digging through the logs but not finding anything.  After reporting what the filters do, they accepted the changes and went to observing.  This is just the opposite of what we should do.  If no supporting evidence is found for the change, reverting to the .snap values is the correct path.  Of course there is some risk to the IFO lock in filter switching, not very appealing after being out for so long.

In the Evening shift operator's summary, The TM ISIs seem to be reported back in high gain:

02:05 Attempt to bring back End Station ISIs seems succesful. GS 13s back to high gain. Seismic graph is showing 3µ/S.

02:09 Ditto for ITMs

02:10  Begin bringing up Input and Output HAM SEI.

02:15 Kissel brought ESDs back and restored ETM alignment.

02:31  All SEI back to nominal isolated states. GS13 gains switched back to HIGH.

This sort of implies the ITMs were put back into High gain but that is not the case.  They were switched to low gain (H1:ISI-ITMY_ST2_GS13INF_H1_SW1R: FM4 & 5 On) 0005 utc and remain there still.  At this point the SDF should have been consulted for proper configuration.

The SEI system is untouch by IFO locking guardians.  SEI SDFs should be green well before looking at going into Observation mode.

One may argue that this difference is not critical: these filters compensate for changes in the analog gain and whitening.  The output level of the filter bank is unchanged.  On the other hand in nominal seismic environment, having greater SNR when digitizing the GS13 signal gives better ISI Damping and Isolation.