Correction: It seems that the tilt maneuver at the end is intentional[1] to not hit the barge full force if something goes wrong. Instead, the control system did not account for (all of the) lag in the propulsion system (time between command and applying force).

[1] based on multiple comments, e.g. https://news.ycombinator.com/item?id=9386127, and a (presumably deleted) tweet by @elonmusk