DHCP display a differences on leases

I have two DHCP servers configured for multiple VLANs. Everything works fine, but I've noticed a strange thing, on the same vlan I find some differences into leases of two servers. Another difference is that a server has filled rispect the other.

What could be the problem?
Lately I have enabled the DNS scavenging and set the lease duration to the default value (8 days).

Thanks