Every time the ASC loop are engaged in full lock (ENGAGE_REFL_POP_WFS) we noticed a large drop in the recycling gain, arm powers and sideband powers.

I looked into the cause of this drop and found that

1. a good power level was recovered when the PRM angular controls were engaged (see the attached screenshot of previous ASC engagement transients)
2. the recycling gain was kicked off the maximum by an excursion of PRC2_Y, which did not have an integrator on for a long wait time

Therefore I improved the ASC engagement in two trials: first by moving the POP QPD loop into ENGAGE_REFL_POP_WFS (so that now the state ENGAGE_POP_QPD does nothing new) and then by moving the PRC2_Y integrator earlier.

Now the transition is much smoother, and we don't loose power anymore: