The Knights at the Kell Echo room do not want to drop dark motes, while every other room was fine for us. The video is just a short example of what was happening to us. The first 6 minutes we got lucky and didn't need any Dark motes, however afterwards just shows how we weren't getting any Dark motes when we needed them. We already reset that room 3 times in an attempt to get some new result, but nothing happened. Unless we are lucky enough to only need light motes, I don't see how this is possible since it clearly favors white motes.