You’re bang on the money; the issue is most likely the bonding of the PU to the aluminum. Do you have any insight into the supplier’s procedure for the bond? The surface prep of the aluminum is critical, since the oxidative layer that forms naturally on its surface needs to be stripped before attempting the bonding. They may be only wiping with a solvent, whereas they need to be grit blasting first in order to be sure that the oxide layer is removed, before wiping with solvent.

Depending on how critical it is for these rollers to perform, you could also ask them about whether they could potentially form some profiles in the aluminum for mechanical locking of the PU in addition to the chemical bonding.