Even in the best pianos, I have experienced that some piano rolls just
tear apart during rewinding, even when foot operated and done very
slowly.

There is really no reason except that the paper has become too brittle.
Bits of paper then often fall off as well, and unfortunately one has to
consider that particular roll a write-off.  Some old books seem to be of
similar paper which breaks when bent.

Kind regards,

Bernt Damm
Cape Town