OSPF advertising loopback network
OSPF will always advertise the networks on loopback interfaces as /32 networks, even if you have configured them with a different subnet. This is how OSPF operates, and it is even defined within the RFC. If you want to change this behavior, you can use the
ip ospf network point-to-point command under the loopback interface configuration mode. This will cause OSPF to advertise the configured subnet mask of the loopback interface.