The guardian script was modified. Often after IMC losts lock the FSS starts oscilating, but the guardian does not notice that in privious script and take time to relock the IMC-FSS.
Now the guardian see K1:PSL-REFCAV_IS_RESONATING channel. That channel return true if the RMS of error signal (K1:PSL-REFCAV_ERROR_RMS) is larger than threshold(K1:PSL-REFCAV_ERR_THRESHOLD)

You can set threshold in the window named CAV_THREDSHOLD which opens with crick on Reference cavity on K1PSL_FSS window.