We've seen lately (since the IMC transmission has been different - see alog 36361 and others) that the IMC won't re-lock itself consistently.  Most of the time someone has to give a kick to the MC2 suspension to make the cavity flash so that it can lock.

Jim and I were looking at it, and it appears that with the different IMC transmission situation, the lowpass that effectively helps the IMC sweep while unlocked (IMC-MCL FM10) was not being triggered properly.  It is supposed to be on when the IMC is unlocked, and off once we get locked. It was properly off when the IMC was locked, but it was flickering on and off when the IMC was unlocked. The FM trigger thresholds just needed to be reset, which included changing the hard-coded values in the IMC_LOCK guardian. 

With one or two unlock tests, the IMC seems to be once again relocking itself reliably.  Please let me know if someone finds that it's not working again.