USG ATP 800 multiple messages "An ip address conflict is detected"

Hello.

We replace our Zywall USG 1100 with new ATP800 with latest firmware.

We got multiples message "An ip address conflict is detected" after replace in ZW logs for each ip addrees in lan.

An ip address conflict is detected. 00:00:00:00:00:00 and aa:bb:cc:dd:ee:ff share the same IP address 172.21.121.100

First mac always 00:00:00:00:00:00.

What is this?