AFTS activation indicates deviation from planned trajectory. It's unusual, being so late in the burn.

Could be a guidance issue, but SpaceX should be pretty good at that by now. Could be engine underperformance, but we got nominal callouts and it would have to be pretty bad for AFTS to notice with minutes left, so that seems unlikely.

I'd guess engine control (due to damage during staging) is the main suspect. We say the thrusters fighting pretty hard there at the end, which supports that idea.