I understand that Musk tweeted that the two engines shut down in sequence early, due to the FAA asking for a lower altitude flight. 12.5K vice 15K. Musk also said that they lacked pressure in the header tanks for landing.
I haven’t seen that tweet. However, that doesn’t change the fact that engine s/n 32 did not reignite for the landing and s/n 36 sputtered during reignition for landing. Only s/n 42 performed well.
Prototype 9 will use engines with more development time so it should stick the landing without exploding due to a hard landing.