Network Device using IP but can’t ping it *** help!

I have a network in place and I statically assign ip’s throughout the network. All of a sudden, a device stops working and reports a IP conflict. When i ping the ip, it comes back dead. I do a mac address search and it also comes back dead. I used IP scan and it also says the ip is dead.
When I try to assign any computer that IP address, it says that it has been statically assigned to another device and cannot be used.

Does anyone have any ideas how I could find the device that is using the IP, even though it won’t ping and comes back dead?

Many thanks