Issue: dupplicate IP Address in DHCP release on Sophos SG330 UTM 9.6.0

I have a firewall SG 330 UTM 9.6.0x and it is DHCP for WiFi ( AP55C)

with network : 172.18.0.0/23

range from : 172.18.0.2-> 172.18.1.254

When i have "Make static" in Network Services -> DHCP -> IP v4 -> Make Static. After that some devices connect and DHCP still release that ip for another devices

So, issue is it release same ip address for 2 devices. The network in 2 computers will be error.

I check numbers of device connect to WiFi , only under 120 devices connect in same time.

I don't understand how can DHCP can be realease same ip for 2 devices and do we have any solution to fix it ?