ISC DHCP 4.4 server giving out leases, but no entries in leases file - where are they?

Running **ISC DHCP Server 4.4**. *(I know, I know, it's EOL...there was a very good reason I uninstalled **Kea-DHCP-Server** and decided to go with it's predecessor **ISC-DHCP-Server**...though I can't recall what it was right now...)* I appear to be getting leases, but the leases file is empty. I cannot work out where the leases are being tracked. dhcp-lease-list shows nothing. /var/lib/dhcp/dhcpd.leases only lists old leases and the file access time shows it hasn't been updated recently. tcpdump -vv -n -i eth0 'udp and port 67' shows DHCP traffic as expected. Scratching my head wondering what is going on.