EX7300 & D8500 IP PREFERRED

I use a D8500 and i assign ip to my device using one lan 2,4GHz and two combined 5 GHz. All the devices are settled with a preferred ip in dhcp with a specified macaddress

I use an EX7300/AC2200 as extender using fastlane from 5GHz to 2,4GHz.

In these way my devices enabled on EX7300 are connected to internet to the ssid generated from ex7300.

Now very often i see that ip generated from router for that device are changed to a new one from EX7300. In this way the devices linket to the wifi generated from externder change ip changing wifi ssid.

To be more clear if i log to the ssid wifi generated from the router they work on preferred ip, instead when i change the ssid using the one of ex7300 ip are different than the ones specified from router.

In the same way the ip used from ex7300 are very often several differents as i can see from genie

How can i solve?

Thanks