alt Hacker NewsEric Berger reports that the fault is likely in the booster stage, not the Centaur upper-stage and not the solid-rocket motors. The means it's either the Vulcan rocket or (more worryingly) the Blue Origin BE-4 engines. If it's the latter, this might also delay the next flight of New Glenn and possibly risk the timelines of the Artemis program.[1]
Irene Klotz reports that this set of BE-4 engines were modified after the New Glenn pad explosion. Specifically, they modified the oxygen valves, which were blamed for the hotfire anomaly (pro-tip: it's always the fucking valves).[2]
The booster shut down about 40 seconds later than the expected timeline, which implies that it had an extra 40 seconds of fuel relative to expectations. It is possible that the modifications somehow caused an under-performance of the booster, which would doom the mission.
I watched the launch until shortly after the solid-rocket booster separation. Up through the booster separation, things looked pretty good. The boosters didn't have any obvious anomaly and nothing was said in the commentary ~ minute after SRB separation.
I tuned out at that point thinking they had gotten past the hard parts. Genuinely surprised to see this news in post.