Hi, I have a similar problem with an android tablet, which changes mac address every time it connects to wifi. If I don't leave wifi always on (to save battery power) it quickly saturates the 250 available IPs on my LAN.
On reddit I found a post where is suggested to remove /etc/pihole/dhcp.leases, and restart DHCP daemon, but this does not seems to work. Where are leases stored currently on Pi hole 4.4 / FTL 4.3.1?