How old are birds and how long have they been laying?
Not common but not unprecedented, new layers can lay some pretty funky eggs in the first month or so.
Check out this weird egg thread...and post your pic there too.
Exactly what and how are you feeding?
There shouldn't be oyster shell in the feed, might be calcium in there tho.
They are 1-2 years old, I bought them from a gal who was rehoming her flock and she had quite a few chickens so she couldn't say for sure how old the ones I got were. I got them in March and they were laying already.
I feed Scratch and Peck non-gmo layer feed which looks like there are in fact pieces of oyster shell in it?? And then I offer oyster shell separately