Problem appears to be clockwise rotation
I don't think it was a problem with legs not locking out, it appears the rocket still has a slight 2-3mph clockwise rotation/motion 'spin' in the final few seconds, that causes a lateral twist to be applied to the landing legs support brackets, which remain in a fixed place on landing, but are unable to absorb this sideways force (been designed to take a downwards force, rather than a spinning lateral one). It almost appears that one of legs disappears, but its the other leg been forced sideways, so that meet.
Take out that spin/body roll, and that could have been a perfect landing. Shame.
Given the stresses on the booster stage, likely to cause even slight deformations (which could affect reuse aerodynamics) around the landing leg bolts/booster body. Spacex's goal may well be to save/reuse the Engline Parts, as the realistic long term goal, rather than re-use the actual booster stage intact, even if the Spacex PR simply says its goal is to reuse the rocket booster stage 'as is'.
It would be a great PR exercise if they did get permission to attempt to land on an US Aircraft Carrier though, would be quite a show. Lets hope that happens at some future date.