From my own experience with a mixed flock of ducks, the Pekins drakes are either the most picked on by the others or the ones doing the picking. I have both here. Chuck the Duck is a little snot, he is always causing some kind of trouble by chasing the others or even just being himself and trying to hang out with the others. He is also the one voted most likely to end up in a dog crate being nursed back to health. Three times now. At 6 weeks Pekins are ready to go and will chase anything that moves pretty much. It could simply be that the others had had enough of him and just put a stop to it. Just a guess, but what you've described sounds like what I've seen here.
