Turns out that I had forgotten to turn the input on for the PR3 P estimator contribution from L (H1:SUS-PR3_M1_EST_P_FUSION_MODL_DRV_L_2GAP) (thanks to Edgard and Brian for having us even consider the estimators!), and that was causing the 0.6 Hz ASC ringups (87658). Even though we're pretty sure we found the cause, we've decided to temporarily turn off the PR3 and SR3 L and P estimators until we're back up and can verify that they are now working correctly.