Something odd is happening with the CM board. Measuring from either input to OUT1 (the "slow output") shows a nice flat response up until many 10s of kHz.
However, when I connect my idependently confirmed 120Hz LPF to either input, the pole frequency gets moved up to ~360Hz and the DC gain falls some 10dB. This happens regardless if the input is used or not, I saw this shape at a tee on the output of the LPF when the other leg of the tee was connected to a CM board input.
This has sabotaged my high bandwidth ALS efforts. I will investigate the board's input situation tomorrow.