I was having an issue where building the lighting was hanging for ~1min at “Starting up Swarm Connection… (100%)”. Turns out this was due to my lovely ISP intercepting invalid DNS requests, redirecting them to an IP that ignores connections on most ports (instead of responding with connection refused), and causing the “swarm agent” to wait for a timeout.
The fix is to double click on the “Swarm Agent” in your system tray, click settings, and set EnableStandaloneMode to True (alternatively you can set CoordinatorRemotingHost to 127.0.0.1, I did both)