Replacement Vulcan test launch with inert payload, experiments, and demonstrations for certification with the USSF after delays caused by payload testing of the Sierra Space Dreamchaser CRS SNC-1 mission, the original planned payload.
Actually rewatching it, it looks like might have been a nozzle failure on one of the GEMs. There's a big flare before clouds obscure the rocket - much bigger than the ice. After this, one side looks to have a bigger exhaust plume than the other, and burns out slightly sooner.
Yeah, NSF are pulling in other angles and it definitely blows chunks and yaws slightly. Centaur burn went long - I wonder if that impacts the second burn.
An SRB blowing its nozzle off is certainly one hell of an "observation". Pretty impressive that the rest of the vehicle was able to compensate for the funky thrust.