They look like the fairing separating. It turns out that if you reuse the first stage, but throw away the fairing and second stage, the next most valuable thing that might be worth recovering is actually the fairing.
They are large, somewhat complex structures. Need to be light, strong and large. There has been speculation that they are attaching thrusters of some kind to the fairings to test different approaches to recovering the fairings from launch.
There has been speculation that one of the recovery ships, based on its location during ASDS operations is trying to recover the fairing if it made it back through the atmosphere.
The beauty of the SpaceX model is that with so many launches, they can keep trying different ideas until they get it just right. Their model includes the cost of the fairing in the launch already, so experimenting with it after separation can be a cheap way to test things that are very hard to test on the ground.
You can see this with their recovery of the first stage attempts, where they kept trying with minor tweaks (grid fins, more hydraulic fluid, better legs, 3 burns, 2 burns, 1 engine burns, 3 engine burns) until they got it right. Now they seem like it is odd that EcoStar 23 will be an expendable flight. Normal has become recovering the stage.