During the re-entry of Stage 1 of CRS-11 at around T+6:02 (58.9km up), an object can be seen enter the camera view in the lower left, and pass the camera a second later (58.0km up). (Images below)
At first I assumed it to be a bird, but they don't fly this high. The object seemed to be traveling roughly in the direction of the Falcon 9, suggesting it was not space debri in orbit. Was this object something that was detached earlier in the launch, or did it break off from the rocket itself? What was it?