After a successful reentry burn of the stage, around 10 seconds after engine shutdown, one of the fins glows red, then begins to burn. My question is why would this burn after the stage already completed to reentry burn to slow it down. And if this grid fin began to burn, why didn't the others?
Here's a picture of the fin just as it began to start to burn.
I know there was already a question about whether the grid fins are flammable but I'm just wondering why they burned when they did and what stopped the others from doing so. I read that SpaceX uses ablative paint on their gridfins which would explain why it is burning in the first place, but why would it do so after slowing down for the reentry burn?
The reentry burn typically happens at around 70-40 km in altitude. I was unable to find data on the rate of descent after the burn.