Swarm error building in UE4

Development Rendering
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1

Hello guys! We have a problem that we cant manage to solve. We are trying to build a large map with many assets, and the build is crashing before it even begins. The error that appears in the swarm agent is this one:

15:46:47: [Interface:OpenChannel] Error: System.IO.IOException: The process doesnt have Access to the file ‘D:\UnrealEngine-release\Engine\Binaries\DotNET\SwarmCache\AgentStagingArea\v1.E21CD36F0EA8C6C8C5310697C9C7C82EAD680461.mtrlgz’ because it is being used in another process.
en System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
en System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
en System.IO.FileStream…ctor(String path, FileMode mode, FileAccess access, FileShare share)
en NSwarm.FSwarmInterface.OpenChannel(String ChannelName, EChannelFlags ChannelFlags)
We dont have a clue what this might be. We have even removed the warnings we got in the build. Every day new assets are added to our large map. I dont really know if its an asset thing.
Thank you very much in advance!

2

I am just guessing though but what usually works for me:
You will have to invalidate your lightmaps to fix this. There is probably an object somewhere in the scene/map that is baked already and causing this. Just as a quick test, try to move every actor with an already built static mesh. And try to bake this on preview. Once it bakes again, you are good to go and can bake again without errors. If you are not under source control to revert the actor movement, try using snap, save the level and move it back to the original position after baking works again. You could also try to duplicate the level and try to bake this one.