The materials used may have an inhomogeneous composition. The plywood may have knots or glue in larger quantities inside, which make burning with the laser beam difficult. The more layers the plywood has, the greater the possibility of encountering a knot. Manufacturers must also use lower-quality wood sheets, which are hidden in the inner layers. Plywood for hobby, special plywood for laser; even if it is more expensive, it is of better quality from this point of view. Try to burn the project one more time, without moving the material, to have complete cuts.
If there are problems cutting on a larger surface of the material, check if the material was at the same height level with the laser head.