Build stuck

When I try to build a scene (including new, empty levels)…a window ‘Build Status’ appear with notification ‘Starting up Swarm Connection… (100%)’ but from now is UE4 stucked…and nothing happens. During this problem my CPU does not even work for 100% as I’d expect. But in past, it used to work fine for me. Is it problem of mine or of the new release ?

I use the latest release 4.7.6.

Thank you for answers

Hello SiCzech,

There is a known a reported issue with the lightmaps of the walls and floors for the blueprint template projects being set too large and causing Swarm Agent and light building to fail or crash. If you are able to reproduce your issue in a blank template project as mentioned, then follow the steps below to fix this issue.

Disable Lightmap Resolution Override

Below you will find the actual Lightmap Resolution for the ‘CubeMesh’ within the ‘Static Mesh Editor’

Static Mesh Lightmap Resolution

Here you can set the value to something like 128 or 256 to get better performance and faster light build times. Let me know if these suggestions helped resolve your issue, or if you need further assistance .


Thank you for answering,
but I have a problem with building itself, and - as I mentioned - it freezes even if I want to Build a empty, blank level. Yes, we also always had problems with lightmaps but well I’m not quite sure if ‘lightmap stuff’ will help me now when I don’t have even any objects in the level…it freezes anyway.

Thank you for the help.

PS: Also, I will wait for UE 4.8 release because - as I said - we didn’t have such problems in previous releases

This sounds like it could be related to Swarm Agent. Would you mind providing me with your ‘dxdiag’ so I can take a look at your system specifications?


I wonder why they don’t update the template to prevent this. Anyway, thanks, you helped me too.

I found the solution. For me all I had to do was check my firewall. These 3 programs had to be unblocked for the build to work:

  • Unreal Engine
  • Swarm Agent
  • Unreal Lightmass

Hope this helps anyone else who comes across this problem