I was trying to play with ci.blueocean.io and nothing was loading. Looking at the chrome developer tools, I see that sse-gateway is causing timeout.
James Dumay and I were chatting when I had that issue, and he said it is working for him. Classic Jenkins UI was working fine, too.
James Dumay sounded like he knows about this lock inside SSE gateway that had caused a similar problem in the past, so this might be a known problem?