I've been closely following the Starship developments. Two take aways was, that the Booster swing around is where things went wrong. While official word not out, appears that it's turn to fly back may been too fast, causing the fuel to swash around inside cutting off fuel and leading to gas getting in it's down comer (wide fuel line) causing the triggering of the charges blow B9 up.
Starship 25....their not sure. She was fine 8 minutes in and there was release gas and everything was cut off. Someone was able to capture picture of the nose of ship flying by itself...Hopefully, they'll figure it out since ultimately this vehicle's later version is the lander to come.