Looks like either Swarm isn’t starting up or the comms are being disrupted. Check to see if Swarm is running when you build the lighting. If it is then it’s probably a port being blocked or some other TCP kind of issue. If it’s not then, well, there’s your problem. Either way, it will be hard to diagnose without more information. Figure our which diagnostic path we need to take and we can go from there.
I can tell you that the one time this happened to me, for some reason the UnrealLightmass project was not being built with the rest of UE4. You could try going into the UE4 project and building it manually (right-click on the project and select Build). Long shot, and assumes you’re using a source-built engine, but worth mentioning.
My scene is tiny and shouldn’t have any issues but it instantly freezes and I have to close UE4 from task manager. Building lighting only used to take a few minutes and it got annoying so I looked for a fix. I seen people say that in Swarm change EnableStandaloneMode = false to EnableStandaloneMode = true. I tried changing it back but got a error message saying: Screenshot - 2ca52dc09dd343b2dd6fe4437bad67bd - Gyazo and it didn’t matter which option I had it on, true or false gave me the same error message.
I asked on Discord and was un able to get this issue solved.
I even tried to create a brand new first person shooter scene and build the lighting in there and it gave me the same freezing issues.
I just loaded the project up and clicked build lighting only again and it froze. So I double clicked Swarm and then it built the lighting and worked. I didn’t change anything beside restarting my PC and that seemed to have fixed it.