As we've been seeing a bit lately, the MC will be locked happily for several hours, but then it will start misbehaving.
Today, I measured the spots on the MC mirrors, and found that the MC2 spot was quite far off in yaw (about -3.5 cm). I recentered the MC2 spot, and then (with the MCWFS on), moved MC1 and 3 until their WFS outputs were close to zero (they had gone up to 100+). In the ~15 minutes since doing that, the MC refl signal is not oscillating like it was, the transmission is up, and the MC has not unlocked.
To reiterate, I did not touch any settings of anything, except the alignment of the MC mirrors to center the MC2 spot, and then offload the WFS. Next time the MC starts acting up, we should measure the spots, and roughly center them, before messing with any other settings. Note however, that this is a ~10 minute procedure (including the fact that one spot measurement takes a little less than 5 minutes). This need not be a several hour endeavour.