Yes, perfectly normal. Chickens are animals and not machines. They are subject to environmental variables that will affect their ability to lay. Too hot? Fewer eggs. Too cold, fewer eggs. Too little daylight, fewer eggs. Too much stress, fewer eggs. Too old, fewer eggs. You get the picture. As an example, my flock of nine layers gives me an average of five eggs per day.
The best things we can do as responsible chicken-keepers is provide them:
Ready access to fresh water and quality ration
A secure coop adequately-sized for the number of chickens so they can rest comfortably at night away from predators
Space for them to run around and act like chickens...whether an appropriate-sized run or pasture (yard) or free range.