The high end? Normally a low pass filter would cut off at the low end, because the cutoff frequency there is so low it blocks everything in the input signal. Unless the pot’s wired the other way around, of course.
If that’s what’s happening then it’ll cut off at a higher frequency when the input signal is higher frequency, so… are you testing this with a low note or a high note going in?
Does it self oscillate at high resonance? If so you can verify which direction the frequency is going, and measure (or estimate by ear) the frequency range. If indeed the range is too low, so the cutoff frequency goes below even bass notes halfway through the pot range, my first guess would be a problem with the CV exponential converter. That’s the 100k, 1.8k, 470R, and 4.7k resistors, transistors, 4.7 nF capacitor, and op amp pins 12–14.
Also:
General advice for troubleshooting a module and asking for help