It seems that whitening gains of some corner station QPDs were somehow set to zero on Friday Feb/20 17:22 UTC (09:22 PST).
Not sure why this happened, this seems to be earlier than the failed effort to update h1imcasc model (alog 89208). ALS QPDs, end station QPDs and all WFS RFs are good. Was something done to Beckhoff that day?
I first noticed this for MC2 trans yesterday because it was interfering with IMC locking and WFS triggering. I checked all QPDs and WFS today and found that the following channels were affected. I restored them all to the value right before it was set to zero.
| channel | old (dB) | new (dB) |
| H1:IMC-MC2_TRANS_WHITEN_GAIN | 0 | 30 |
| H1:IMC-IM4_TRANS_WHITEN_GAIN | 0 | 18 |
| H1:ASC-AS_C_WHITEN_GAIN | 0 | 18 |
| H1:ASC-OMC_A_WHITEN_GAIN | 0 | 27 |
| H1:ASC-OMC_B_WHITEN_GAIN | 0 | 27 |
Trending the uptime of the Ethercat system, slow controls were restarted and came back up two seconds before the time listed in Keita's alog, likely a part of Daniel's updates to include CHETAX electronics (alog89211). Settings may just have not been fully recovered after that restart.