B20 DHCP seems to not hand out a range of IPs

I’ve been watching my dhcp client list due to some devices not able to get IPs from the dhcp server. I shortened the lease time to try and address that issue but noticed that the dhcp server seems to be skipping the .170 to .189 IP range. We don’t have any dhcp reservations so I’m curious as to why this is happening and what I can do to free up that range of IP addresses.