A client cannot see the enterprise SSID while other clients remain connected. What is the cause?

The correct answer is that the hidden SSID was not manually configured on the client. When an SSID is hidden (non-broadcast), client devices cannot discover it automatically. They must be manually configured with the exact SSID name to connect. Since other clients are connected, the network itself is operational. The client having incorrect credentials (for either broadcast or hidden SSIDs) would typically result in a connection attempt failure, not an inability to see the SSID. A broadcast SSID, by definition, is discoverable, so it wouldn't need manual configuration to be seen.