This can be caused by IPv6 being enabled along side IPv4. Ambari-Agent does not function properly in this scenario, and will attempt to communicate by IPv6 despite it not being used.
This should be addressed by disabling IPv6:
1) Add the following to /etc/sysctl.conf to disable IPv6 on the machine:
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
2) Reboot each machine.
Ideally this should be done for all machines in the cluster, and not just those being registered within HDP, in order to prevent future issues.