You are right, there is a very tiny glow about 8 second before the anomaly, that intensifies during the final 1.5 seconds.
Its not much, just enough to reflect some sunlight on the shaded side of the second stage - but at that optical quality, it could also be caused by an antenna (or anything else protruding).
Yes, it could be something else, maybe some frost or ice still attached to that zone. We'll have to wait and see what comes out of the investigation.
Anyway, that's enough fun for today, I have to back to studying. :facepalm: