Thank you for sharing the solution.
This comes from standard n8n. On init, n8n looks for the tunnel subdomain in the env var TUNNEL_SUBDOMAIN_ENV, else in the tunnelSubdomain key in ~/.n8n/config, else it creates a random string and stores it in the tunnelSubdomain key, and uses this when creating the tunnel.
The problem is that, when localtunnel is interrupted, it can fail to release the subdomain, so creating a tunnel with an existing subdomain results in a new subdomain in the format {adjective}-{noun}-{number}, which is set by the localtunnel server. This is an open issue in the localtunnel lib. As a workaround, you can change your subdomain in the tunnelSubdomain key to a new one, or delete it so that you receive a new random string on init.