Agreed--everything looked good. Booster engine cut-off was ~40 seconds late, though, and stage separation happened lower and at a slower speed than normal. I think at that point, something happened with the Centaur/payload. Either it couldn't handle the aerodynamic forces or maybe it deviated from the corridor and FTS fired.

The ULA animation also showed some strange rotation at stage sep and maybe even a faring bump the Centaur (knocking it off a bit).

Maybe the underperformance of the booster left the upper stage too low and atmospheric drag caused problems at stage separation.