SpaceX had successfully landed the Falcon Heavy center core but the center core fell over and into the sea due to large waves.
SpaceX was able to recover the two side boosters and the payload fairing.
SpaceX uses an Octagrabber robotic system to stabilize and hold recovered Falcon 9 boosters. However, the center core has a different shape which did not work with the Octograbber.
In a statement, SpaceX confirms rumors that the center booster core from the Falcon Heavy Arabsat-6A mission toppled over the weekend; crews could not secure the booster on the droneship in rough seas with swells as high as 10 ft (3 m). Doesn’t affect future missions.
— Jeff Foust (@jeff_foust) April 15, 2019
SOURCES – twitter
Written By Brian Wang, Nextbigfuture.com