Like Amy, I'm thinking the 'problem' eggs have all come from the same hen, which to me would point toward a genetic weakness.It is usually the cause and often with shipped eggs.
I do not know what is happening with the eggs that are not shipped, maybe the hen is laying eggs that are not complete.
If she finds out that the eggs are from more than a single hen, then I'd be wondering about the rooster, or perhaps an unknown dietary deficiency.
Make sense?