Here is the waveform across the fet source and drain with the probes held firmly against the work, making a good weld.

Notice the 40.8v spike on this waveform. It was caused by the probes not being held tightly against the work. The fets have a 75v internal diode that should protect them. But it has been recommended that a schottky board be installed per the note from the designer, to attenuate these spikes to help better protect the fets.