As Jaykay really. We get the occasional egg that is super big, super small, a bit rounder than normal, etc.
We have found that a certain batch of hens have tended to lay certain shaped eggs. For example, we had some hy-lines who would all lay really big, very round eggs and some black rock who would lay more elongated eggs.
Are your birds fairly young and so their eggs are changing from the smaller type egg that a POL pullet normally produces to the egg of a more mature laying bird?