We eventually discovered the problem / solution. We on a security appliance from Palo Alto Networks that was blocking PCoIP 5.2.0 traffic but not PCoIP 5.1.3 traffic.
According to a Vmware backline engineer:
"A change was made to the ephemeral TLS connection that is used to establish trust and negotiate network parameters for the subsequent UDP traffic. This change allows the customer to use their own TLS server certificate for this connection. For details of what happens during PCoIP setup, and how this changed in View 5.2, see KB 1038762."
It appears that Palo Alto Networks didn't like this change. When we removed our Palo Alto appliance from the WAN, PCoIP 5.2.0 connections could be established. We eventually had to create a rule to permit the Category: private-ip-addresses and URL: pcoip-default-sni/. Once that change was made, WAN PCoIP 5.2.0 connections began working.
