To see if there is a duplicate IP address a handy tool is arping.
ubuntu:$ arping 192.168.1.83
WARNING: interface is ignored: Operation not permitted
ARPING 192.168.1.83 from 192.168.1.86 eth0
Unicast request from 192.168.1.73 [00:26:C7:D0:93:D2] 203.042ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.304ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 4.564ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.706ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.247ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 38.680ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.389ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.622ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.929ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 4.700ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 3.911ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 6.664ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.071ms
Unicast reply from 192.168.1.83 [00:26:C7:D0:93:D2] 5.526ms
^CSent 15 probes (2 broadcast(s))
Received 14 response(s) (1 request(s))
If there is a duplicate IP you would see a reply from two seperate MAC addresses.