I adjusted the setpoint of the diffracted power slow servo in the ISS second loop to H1:PSL-ISS_SECONDLOOP_REFERENCE_DIFFRACTION_CAL_OFFSET = -5.32

I could then engage the ISS second loop without problems by switching on its input. No visible fluctuations in the diffracted power.

I tested once a full lock acquisition, up to PREP_DC_READOUT_TRANSITION with the ISS second loop on.

The ISS second loop can also be engaged with the IMC guardian.