the reason

Too much tension on the core paper roll

Because the spray device sprays too much steam, the core paper is too wet.
Or gluing device causes the corrugation of any nip

Double-sided machine upper and lower conveyor belt tension uneven (slanted corrugated)
Low-level, flattened corrugated

Core paper's compressive strength is too low

Measure

Reducing the brake on the paper holder Check the position of the pre-processor, drying, repairing or replacing the drive engine of the pre-processor. Reduce the amount of steam injected on the core paper. Ensure good adhesion and warpage. Reduce single-sided cardboard and The humidity of the double-sided paperboard or one of the glued-up core paper rolls is too high, reducing the amount of steam sprayed or turning off the spray device or replacing the core paper roll to keep the belt speed constant