What is this? Candling.
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That's strange. I haven't seen anything like that. Here's a wonderful link to check the progress of your eggs:
If you look, the day 7 egg here and yours don't quite look the same.
That may be the start of some bacteria growth. Or the embryo recently died and that's the start of the blood vessels breaking up. Are the veins as defined in that egg as they are in others? I've noticed that some with start to fade before they completely dissipate. And if it is bacteria growth, the embryo could live for quite a while before it's completely overwhelmed with bacteria. I would try to keep that one a bit separate from the others, candle that one last, and wash your hands after touching it/before touching any other eggs.
I'm sorry to hear that. Good luck with the other eggs!