Carrier-grade NAT is a practice by ISPs that allows them to share small pools of public addresses among many end users. I believe that in certain circumstances, carrier-grade NAT may affect the stability of webcocket connections, possibly in non-trivial developer setups or otherwise. Some time ago, I was observing constant interruptions of websocket connections. I called my ISP and they told me that they were aware of the problem, explained it was due to carrier-grade NAT, and upgraded my subscription. No more carrier-grade NAT, now I get assigned a public IP address that is not shared (still dynamic though), and that was the end of the problem.
Unfortunately, I am fuzzy about the details since that was some time ago.