I don't know how long your hen has been laying, but this is fairly common with pullets just starting to lay. The egg laying process is pretty complicated. That doesn't just include how they put the egg together but when and where to lay the egg. To me it is amazing how many get all of this correct right from the start.
Often about a week before she starts laying a pullet starts looking for a good place to lay the egg. When the egg is ready she goes there and lays it. But all of them don't so that. It's as if the egg shows up and she is not expecting it. She pops it out wherever she is. As long as the eggs are in random places I consider these to be oops eggs, she doesn't have control of the process. If the eggs are consistently in one place she has decided that is her nest, wherever it may be.
There are certain triggers that tell her when to release a yolk to start that egg making process so the egg will be laid during daylight. When they start out laying those triggers don't always work right. The egg may be ready at night so you may find an egg under the roosts.
Usually if they are having these issues a pullet debugs her egg laying process in a few days and gets to normal. But these start-up issues can be frustrating when they show up.