I have diagnosed the cause, the dead hearthling goes the settle the big Beyond/Heaven/Skies which is actually your RAM and starts building most lavish city ever, taking all those sweet random access memory resources to do so.
What I did is I created a new save completely random as I had no intentions of keeping it, place town flag immediately, went to harvest, mine tunnel tool, selected a huge flat area.
As soon as they started to mine the 200 x 400 some odd area the game went to 99%
lua and 3% FPS, the game stayed at 60 fps in camera movement and fluidness.
I thought that was interesting it doesn’t happen with forest clears, it only happens when mining, and it gets worse if you dig several layers deep (like 200 x 300 x 12 downwards).
The game becomes unplayable with one herthing at max range of 1600 x 1200 x 1 deep, in fact it crashes with an unhandled exception, I can attempt to repeat this if you would like for the dance. Just let me know I’m down for serious bug re-creations if necessary Transcribed with Dragon NaturallySpeaking