Might be the cloud layer
I thought it might be a large chunk of ice breaking off and impacting the corner. Seeing the replay, it does look like a pretty violent event.
I also thought that the first stage burned ~20 seconds longer than planned, but it might have been that the audio and video were out of sync.An exploding turbopump could also explain that.
"Corner"? Something seems to disintegrate right at +1:20. MaxQ, "vehicle is supersonic" then poof. Looks too rough to be a shock ring type effect.
Engine one anomaly.
I called it first: turbopump exploded.