UE4 Suck on 100% Exporting Lighting Data but still running?

So this is my 5th attempt to re-build lighting on my level which is a decent size. There is lots of foliage and trees in the map and its set to a sunset, I’ve attached some images below as to what I can see happening with the “Swarm” and my UE not responding but still running some how, I’m rebuilding on Preview quality also.

Specs: Nvidia GTX10606gb, 16gb Ram, i5 4590k, 1tb HDD

I’m happy to learn a new way to rebuild my lighting but I would like to know what is happening here so I can understand how to fix it in future.