The guardian that toggles the FSS gain when it is oscillating has not been toggling it, which is why it has sometimes been taking a long time to lock the FSS and IMC.  The reason it wasn't working was that it relies on H1:PSL-FSS_OSCILLATION to check if the FSS is oscilating, which wasn't working.  I reset the threshold for that from 5V to 0.2V, and now the guardian is toggling the common gain to relock the FSS as it was meant to.