On the YouTube video, they were still showing the graphic about the region of maximum aerodynamic stress at the time of the anomaly.
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I wonder if the first stage engines didn’t throttle down correctly, the speed could have put too much pressure on the upper stage.
It actually was past Max Q.
I’m think the RSO initiated the Flight Termination System or the upper stage had a major problem. It’s still possible there could have been a structural failure that didn’t show up until after Max Q.