Build times some cores take longer

Hi, this is just curiosity but I’d like to know what’s the potential cause.

When building you can see in the swarm agent the cores or threads of your CPU processing, sometimes I see the majority of the cores finish their part in say the “Processing Mappings” part but one or two are left processing almost as long if not longer than the entire build up to that point.

Is this due to one thread getting stuck doing one large ■■■ lighmap in the scene? or a mesh with bad UVs?