Weird behavior from mki x es.edu DIY Kick Drum

I've built a few DIY kits and have never run into any issues until now. And I'm not even sure if I messed up the build or the design of the module is just wonky... Turning up the decay past 11 o'clock or so causes the volume of each hit to vary, and fluctuate wildly if turned up all the way, as can be seen in the image.

I can sorta replicate the issue in the simulated circuits linked in the manual - it seems like the volume of each hit depends on what direction the wave was moving when a new hit is triggered. In some cases the volume goes up, because of resonance, in others it goes down as the newly triggered wave is muffled by being out of phase with the previous one. Interestingly the issue disappear of the pitch is turned all the way up.

Anyone else having this issue, or did I fuck up the build?