I had the same issue once upgrading my nodebb installation from v1.4.2 to v1.5.1
The trick that worked out for me was to remplace the ip address in the "url" segment by my domain name in the config.json file.
Have you tried that out?
Check out this topic https://community.nodebb.org/topic/11324/error-listen-eaddrinuse-0-0-0-0-4800-looks-like-your-connection-to-nodebb-was-lost-please-wait-while-we-try-to-reconnect/9
changing for example,
"url": "http://localhost:4800", or "http://124.129.xxx.36:4800"