The satellite antennas used to uplink a video feed like this have a very small beamwidth (around 1° depending on antenna size and the frequency they're using), so you need to keep them pointed precisely at a specific point in the sky. They rely on a sensitive IMU (accelerometers) and fast motors to actively track the satellite while the platform moves. They're quite impressive to watch in action[1], but I'm guessing they're no match for the shock and vibe of the rocket landing.

1: https://www.youtube.com/watch?v=k79vfwUkeYk

They use a satellite link on the barge, and the vibrations and pressure from the landing booster almost always cause the link to drop until things calm down.

They have said in the past that it's "solveable", but it's not exactly a high priority by any means as they can always retrieve the footage when they get to the barge.

According to the SpaceX media commentary folks that were talking as it was happening, it's because "intense vibrations are interfering with the antenna".