Quick update - The issue had nothing to do with Cloudron server and everything to do with the Nginx Proxy Manager host sitting in front of the Cloudron server.
Good time to mention that NPM in front of a Cloudron server is not an officially supported Cloudron setup.
Yet, with this being said, once Websockets relay was enabled on NPM proxy host, everything fell into places.
Many many thanks for @nebulon and the cloudron team for their support as always.