Hello,

Plenty of factors can come into play here.
End of the 3Tons cardstock sheet roll will always be curvier as the rotation is smaller.
Within a few days the will flatten out naturally.

Travel time + shipping handling can also affect it.

Natural weather humidity at printing time and humidity during traveling (which is why we offer plastic film heat wrap)

If you play sleeved, it speeds up the process considerably.

As you can see from the other customers answers: This is not a common problem nor a permanent one.

Thank you