Isolate the problem, whether its SCF-boards or turbo/gssl-sc.
Double check for same signal level at both SCF-boards outputs (before the 47K summing resistor on SCF-pcb) and for a seperate signal feed per each SCF-board. You might have a provision for gssl-/turbo-mode switchable and wired the differing SCF-board input resistors (10K/20K) wrong.
Identical parts and parts values on turbo pcb and GSSL sidechain ? (both pcbs fitted with quad opamps LF347 instead of TL074, same type VCAs, 10Ks between VCA-pins 3/5 not fitted, VCA-pin4 connected, ...).