I was experimenting with newly created virtual machines, but on a rather small subnet with not that many IP addresses in the DHCP pool. When the pool is completely used by old VMs which don’t exist anymore, the server stops handing out IP addresses.
It would be good to have either an option to delete old active DHCP leases (to free up some space in the pool) or have the DHCP server to check whether an IP is still is use (using ARP), freeing up the IP in the pool if no one is using it anymore.