From what you are describing, it seems like it’s working as it should. The mix knob is behaving correctly…when it’s turned to one side or the other it causes only one side to pulse while the other lets the signal through without pulsing. When it’s in the middle position (12:00) both sides should pulse the same amount.
This is making me wonder if you had the mix knob turned to one side when you recorded the sound sample. Can you test that again with the mix knob in the middle?
If you are looking for the pulsing sound, the phase switch needs to be set in the “in” position. Once you get the pedal working correctly, you’ll probably need to adjust the tone trim pots (high and low) to dial in the proper amount of both signals.
-Brach