Despite metrics showing traffic for an agent, and it otherwise appearing in the Team Center topology, related Experience Cards have "no traffic" on them.
Team Center 10.x with 9.0x and 8.x agents.
8.x Agents in the network topology
This was caused by 8.2 .Net agents providing information to the Enterprise Managers - though many features will work with old agents, they are not fully compatible with Team Center and not all functionality will be available - such as Experience Cards - as they depend on newer agent features that were not present in the 8.x version.
Upgrading the agents to a newer, supported version will resolve the problem.