Root cause!

Detailed analysis of the telemetry that was available led engineers to conclude that there was an “unexpected electrical arc” within the power supply for the upper stage. That shorted the battery packs that power the upper stage, causing a loss of power.

Beck said that arc was the result of several factors. That included a “ripple voltage” in the power system, the presence of traces of helium gas and an “undetectable” flaw in insulation in the power system. Those factors combined, under conditions governed by a relationship called Paschen’s Law, to create the arc.

Great investigation work by the team. That's a pretty impressive turnaround for a return to flight (2 months).