Sorry to trouble you. I built the version 2 Drop Controller breadboard version) some time ago and am having excellent results with it, so I am extremely grateful for all your hard work and for the fact that you have been willing to share it with others.
However I thought that I would now try and build V3 on a protoboard and would be grateful for a little clarification. I noted that you had found an issue in the circuit diagram and updated it on 18/05/19 but I am a little confused with regard to the wiring of the auxiliary triggers. In the upper right of the circuit diagram you show the connections to the 3.5mm jack stereo socket viewed from the top and I can confirm that is the same as the ones I am using.
According to that diagram the Right Hand rear pin connects to the mid point on the jack plug which according to circuit diagram is the data line. The Left Hand rear pin goes to the tip on the jack which according to the circuit diagram is VCC. The circuit diagram also shows that the resistor is on the data line.
However when looking at the images of the breadboard version and protoboard version the data line from the Arduino appear to go to the Left hand rear pin which is the opposite of the little diagram of the jack socket in the upper right hand corner of the circuit diagram.
I would be grateful if you could clarify which is correct and I apologise in advance if I am misreading something here.