It looks like your code is okay, but a few things I can suggest for trouble shooting.
I don’t think you mentioned above, but is resonance working, just not cutoff?
Also, you can try to confirm the the AnalogControls are working as expected by doing a simple linear scale/offset with its output before using the parameters. Something like:
float cutoff;
cutoff = 500.f + (knob1.Process() * 12000.f);
flt.SetFreq(cutoff);
One other thing that doesn’t necessarily have an effect on whether it works or not, but makes it a little trickier to find where the issue might be, is the scope of variables. Many of the globals are correct, and/or necessary, but a few of them make it a little harder to trouble shoot (like freq and res, that seem to only be needed in the UpdatePotentiometers() function).