I am sorry to hear you are having a similar experience with these birds. I am equally saddened and frustrated with this behavior. We did make a change in our feed (increased protein), checked repeatedly for external and internal parasites, started spreading out the feed on the ground to give them something to do, throwing random food snacks in, put a rubber ball into the pen for them to play with, grass clippings, mineral supplements, kale, seaweed, and meal worms. I don't even think free ranging them would stop this, as they tend to do it the most a bed time when everyone is on the roost bar.
By crossing these with my Barnevelders the new birds I have gotten are so calm and friendly it is wonderful. I am thankful I purchased the Sapphire gems but they certainly are not something I would choose to purchase again. I will be keeping a few to continue crossing them with my Barnies because the cross birds are great, but I will probably be freezer camping all but 3 or 4 of them. I know it's difficult to know when you get a sex link what to expect but this kinda of behavior caught me by surprise. I believed it must have been something in their diet that drove them to this but even feeding 20% feed with supplements did not stop the behavior as they will pluck any chicken that they can catch unaware. I too worry if I put any other birds in with them that they will learn this behavior so mine will be permanently in a side pen set off from my main barn.
Here is a pic of the cross chicks:
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