J. Kissel, E. Goetz, L. Dartez

The lock loss at 2025-01-23 16:41:17 UTC (08:41 PDT Thursday morning) was a a result of our first attempt to turn ON the additional 65k to 16k digital AA filter (see LHO:82404 and references therein). 

Out of the utmost precaution we (via command line) performed what we do all the time (via script) for a analog whitening filter change: 
     - via command line, ramped all DARM error signal over to DCPDB by simultaneously changing the gain the 16 kHz filter banks (H1:OMC-DCPD_A_GAIN and H1:OMC-DCPD_B_GAIN) from A:1.0 and B:1.0 to A:0.0 and B:2.0 with a ramp time of 10 seconds. 
     - switched ON the second copy of the 65k to 16k "Dec16k" filter in FM10 in the 524 kHz filter bank for A, H1:OMC-DCPD_A0
     - command line ramped all DARM error over to DCPDA, from A:0.0 and B:2.0 to A:2.0 and B:1.0 with a ramp time of 10 seconds...
... and it was most of the way through that 10 second ramp back to the new filter configuration of DCPDA that we lost lock.

We're going to try again, but this time have the new AA filter configuration on already during lock acquisition.