Greg (Strider) Moore asserted that:
No details at this time:
https://twitter.com/nasaspaceflight/...848960000?s=21 about 34
seconds in.

And scroll to 1:49 PM he
https://www.youtube.com/watch?v=5QbM7Vsz3kg

Appears to have occurred after engine shutdown. Several seconds later,
venting from more than the designed vents, and the cloud eventually lit
up.

SN4 cylinder appears to still be a cylinder, but rather horizontal.

/dps

--
Trust, but verify.