Styrofoam in your seat provide great protection but can also quite easily break. Fortunately easily replaced in most seats. Styrofoam will usually break when seat is carried or moved. Relatively often also when parent or toddler lean too hard on some sensitive spot. Styrofoam is attached to the seat with tejp and glue or often also only with tape.
Todays Axkid Minikid 3 has styrofoam which is easy to replace. We do it quickly in our workshop or customer can make the replacement. Some glue and a screwdriver is all you need.