Please Help!! What happen? (Lightmass crash)

I’m new to UE4, facing the problem about light build.
Right now I’m doing some exercise, after pressing the Build button, a Message Log appear, it shows the Lightmass crashed. Why??
Can anyone help, please.

I get this error semi-regularly. The fix that works for me is to open up Swarm-Agent (in the taskbar) and then clean cache and validate cache within Swarm-Agent.

Hi scragnogg,

Thanks for the reply!
I follow your method and the problem is solved. Thank you.

I have the same problem and my meshes are all low poly!!! SO strange. I can’t find the swarm agent on the task bar. Where can I find it exactly? Thank you.
Got it! It’s in the UE4 engine - binaries folder

Hi there ,
You should see the swarm agent when you start to build .
View by clicking here :