I previously thought that the middle core on a Falcon Heavy was expendable. So it not landing (while needing 3 engines) makes sense, as it was only a week or two ago that they tried a fast/hard landing with 3 engines over open water (as they weren't sure then that it would work). I would expect this landing mode to need at least a couple more tries to get working reliably.
Well that test was unrelated. They only reason they tried that with an ocean landing was because they wanted the barge for the FH demo flight.
This should have been a 1-3-1 style landing burn where it lights up one engine, then 2 more to slow it down, then drops down to just 1 again at the end. In this case it sounds like the the outer 2 engines didn't start up right, so it came in way too hot.
They also have said that the center core of FH is basically a new design from the ground up, so it makes sense that they had some problems on it's first landing.
