On tunneled connections, the ServiceManagerDialog V12.1.x or newer cannot connect to a ServiceManager instance, where older versions wok flawlessly on the same machine.
The difference between 12.0 and 12.1 and newewr of the ServiceManagerDialog has been the introduction of support for IPv6.
Since 12.1 the operating system default of the IPv6 dual-stack is being used, whereas 12.0 has been using the native IPv4 interface.
Release : 12.1+
Component : ServiceManager and ServiceManagerDialog
As the operating system's basic networking layer is being utilized, no tracing from application side is possible. In-depth analysis can only be done at the OS/networking layer.
Please check with your OS/network administrator how the routing/tunneling is actually configured and how it needs to be modified to work with the dual-stack.