There is a bug that the Auto_Pulse feature will not work correctly when using the Spot Welder with the Diode Set. Read more how to easily avoid it when building the Spot Welder yourself.
The bug is that the AutoPulse feature will only do one or two welds and then stop working when using the Spot Welder with the Diode Set. This is due to the leackage current of the shottky diode that always creates a voltage on the Arduino AutoPulse pin. The resistor R15 is there to drop this voltage so the Arduino sees a valid low signal. Problem i found is the 620Ohm resistor is just a little to big to drop the voltage enough.
Pupulate R15 with a 470 Ohm resistor instead of the 620 Ohm. Then everything works fine. The BOM on Github for V2.2 has been updated with a new column “PCB Onprint” to make clear which parts to use on the PCB assembly.