In the PaaS one of the components in the stack is the GCE load balancer. This service recognizes websocket connections separately from regular http/https and has a connection timeout specifically for it. However, this timeout appears to be on the lifetime of the websocket connection rather than its idle time. With the default value of 30 seconds this means that the connections between the RCS and IDM are forcibly closed after 30 seconds regardless of the traffic that may be on the connection. The pong interval has no effect on this behavior. A separate bug is to be filed with Google to address this.
A side effect of this is that the RCS does not reestablish connections closed in this way. It does recognize the closure and logs the event but the only way to reestablish the connections is to stop and restart the RCS. These connections should be auto-reestablished.