J. Driggers, S. Dwyer, J. Kissel, B. Weaver

In our continued broad sweep of understanding what's going wrong with the IFO, we found that SR3 was unexpectedly moving by ~14 urad (measured at the top mass), ~6 urad (measured by the optical lever) just after lock loss, and then restoring its position after the completion of the ISC_LOCK guardian's READY state. 

We traced this down to the Lockloss Trigger (see initial release aLOGs in LHO aLOG 44838 LHO aLOG 45061, and ) being errantly enabled on all stages of the SR3 -- which normally does NOT receive any ISC control, so there's no need. The move was because the SR3 CAGE SERVO (unique to SR3) uses the M1 DITHER PIT OFFSET (H1:SUS-SR3_M1_DITHER_P_OFFSET) as its actuator, which is upstream of the M1 ASC trigger. That cage servo is typically outputting 32 DAC counts ("should be" 85 urad in slider units ... but apparently it's not that much), so halting that output via the lock-loss trigger moved the suspension, and then it was virtually immediately restored upon clearing the trigger in the DOWN state.

Turns out this had been happening since the development of the trigger circa Fall 2018, we just never noticed.

We've now disabled (set of OFF, or 0.0) all of the following channels:
    H1:SUS-SR3_${M1,M2,M3}_TRIG_${LSC,ASC}_ENABLE
and accepted in the SR3's safe and OBSERVE.snaps, so this should not happen again.

#RedHerring