It seems the ISM array is invalid because it’s not rendered on Dedicated servers, GetStaticMesh()->HasValidRenderData() &&
A “quick” and dirty fix for this is simply not removing the instances on the dedicated server, your characters will still collide with invisible meshes, so you’ll have to setup custom collision channels for this.
But considering you are using Dedicated Servers, you already have the source built version of Unreal Engine on your computer, so applying the fix that was supplied in that post is fairly straight forward.
