VPIN_OUT PWM is tied to Arduino's internal timer, which controls delay(), etc.  Default runs at ~1 kHz, which is a bit slow for VPINout.

Consider changing VPIN_IN LPF to 10k + 100n
Don't increase tau on VPIN_OUT, because it's already 10 ms... MCM throws an error if it takes too long.

Consider swapping mega P12 with mega P4, so VPIN_OUT can use MEGA P12 PWM.

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Solution:
VPIN_OUT_PWM now connects to MEGA P12
VPIN_IN_NOISY LPF is (768 Ohms + 1 uF) 