Elon mentioned the problem was that they ran out of hydraulic fluid about 30 seconds too soon. The rocket had to try to right itself using only engine gimbalin

Elon mentioned the problem was that they ran out of hydraulic fluid about 30 seconds too soon. The rocket had to try to right itself using only engine gimbaling instead of using the waffle paddles, which didn't work out so well. The great thing is they've already fixed the problem for the next flight.