WAVE stage transition issue

Hi all, I've just finished building the lovely little ST WAVE. Nice easy SMD build, took me about 90 mins.

I don't have the schematic so I'm not too sure how each wave is formed but on mine, the first wave stage W doesn't decay gradually, rather it just stops with zero decay and the next stage A begins. With all pots on the slowest settings apart from V in the fastest, (100% CW) , the two middle stages seem to hold for way to long,

Is anyone able to point me to the right area for a 'focussed' reflow, to potentially fix the issue please? At a guess, I'd say that a capacitor associated with W decay stage isn't working as it should, thus affecting A and V behaviour. Movie attached to illustrate what I'm struggling to put into words.

Thanks, Will