I think it is because the multiple installs were not completely uninstalled according to https://docs.splunk.com/Documentation/Forwarder/7.0.2/Forwarder/Uninstalltheuniversalforwarder
Following the doc above and rebooting the machine should do the trick.
Are you running more than one forwarder on a machine so that the same hostnames show up as duplicate deployment clients?
If this is the case, you can set different servername and default-hostnames for your forwarders on the same machine to differentiate your forwarder clients.
splunk set servername <new_servername>
splunk set default-hostname <new_hostname>
For example, if you have two universal forwarders sending data from the same host named my_host, you can set both the servername and default hostname of the first forwarder to my_host_uf01, and those of the second forwarder to my_host_02.
Hope this helps. Thanks!