Advance ip scanner finds fake pc/ip in my LAN that create conflicts

Question

n my network some PCs have been physically relocated after formatting, assigning new name and new ip (fixed ip usage on each client - no DHCP). The IPs that were them in the previous "life" were assigned to other new machines. Now, however, these PCs (ACER) continue to provide (making a scan of the network) a fake "presence" with their old ip and consequently create a conflict to new PCs that have inherited from them the ip. In the image you can see clearly (in blue) the pc (old) with their new ip and the same (fake, in orange) with the old ip. I tried clearing the cache, reinstalling the network cards, cleaning up the registry.... nothing to do. I also find them in the list when computers are off. They disappear only if I physically disconnect the network cable. PCs are not pingable by the ping feature within Advanced ip scanner. I don’t really know what to do anymore.