Upper L corner, 100uF:
"Added this to filter out AC
that was getting in this DC
line and wreaking havoc
"
..you
don't want this extra electrolytic here, it messes seriously with your time constants and upsets the current-drive opamps. If there's excessive AC component here, it have to come from the sidechain or driver
Current through reactor/attenuator is differentially driven between 1) U3A, TL084 Pin1, adjusted through RV#3 and 2) driven from inverting amplifier U3D, pin14
this also drives panel meter
Input signal for all this comes from time constant C11/R23, following the rectifier based around U2 - which again receives its input signal from the input highpass/bandpass filters centered around U1 (that makes the sensitivity emphasis for the rectifier and attenuator)
check that signal here resembles what happens at ic U3 pins 1 and 14 are looking right, following hi-freq content
If it was me fixing this, I'd shotgun the three TL084's, starting with U3 - those jfet thingys don't like driving inductance. Make sure to socket, so you can experiment with alternative opamps.
/Jakob E.
PS: Posted the inspiration for this, the Ortofon STL-631 Cutting HF-limiter (de-esser) here:
https://groupdiy.com/threads/ortofon.88483/
PPS: MagAmps are cool