Yes, it sometimes happens that abnormalities occur among new layers until their bodies develop a rhythm. These glitches are not normally something you need to be concerned about. However, in rare cases they can be a harbinger of trouble.
What you might wish to do is to spend more time with your new little flock and "spy" on your layers when they're in the nest so you can begin to associate the different eggs with the hen that laid them. Each egg will have subtle characteristics that become a signature of the hen that laid it.
In addition to this, you will learn what normal behavior is for each chicken and when a problem is developing you will be more likely to catch the clues so you can intervene before it gets serious.
Signs to watch for are a hen that may spend much too long in the nest box and not lay an egg, lethargy, self isolation, tail held down low and flat, feathers fluffed and shoulders hunched. There may be a discharge from the vent. Poop may change to runny and full of mucous. Appetite may be poor.
The double egg you found is most likely a one-time event. But watch for a hen that lingers too long in the nest as she may have just laid one egg with another one close behind. This is not normal, and a second egg in the same 25 hour cycle is more apt to get stuck and cause egg binding. If you so much as suspect this is occurring, immediately give the hen a calcium supplement, one tablet directly into the beak. This will help her contractions and boost the calcium in her shell gland to help prevent the egg from getting stuck, which can be life threatening. This is the calcium I recommend.
