@ARGamingPK1 

David can correct me If I'm wrong on this but Deco units in Access Point mode will not assign IP addresses; the router you have connected to the Deco system is responsible for the DHCP function.

The only thing I can think of is that the DHCP server on the deco for some reason can’t talk to your splitter and that’s why there is the IP conflict.

There are two ways you can test this IMO

1. Remove the splitter and test in both AP mode and router mode. If the issue goes away in both modes, then it’s the splitter if you have the issue still its either the device itself or the deco
2. Replace the splitter with the LS-1008G switch you have. It is on the list of approved switches for ethernet backhaul

Here is the list of tp-link switches combatable with deco ethernet backhaul.

This link https://www.tp-link.com/us/home-networking/all-soho-switch/ was taken from the following post https://community.tp-link.com/en/home/forum/topic/98898

  @HelpFixDecoApp I think my issue is fixed after i set static ip address of Ethernet Backhaul Deco Unit in my Main Deco Unit. I will let you know in few days. @David-TP 

  @David-TP Any suggestion?