After playing for a couple of hours on a new save with mods, the game started to lag: 80% Freeze, 20% Play
I activated the "Show Time Usage" in the debug options and saw that Renai took up 98% of the time.
This started happening after I deleted an underground belt, but I don't think it is related.

I uploaded the save here: https://www.dropbox.com/scl/fi/4amo46yh2sexpifl6oz5n/Bored.zip?rlkey=n0c6epp9qi37bl2ed3kya9rnv&st=dxqqakp7&dl=1

It looks like in your top right Factorissimo building, there's a thrower inserter that's set 1 tile off the Hatch and is continually spilling steel on the floor. The floor is covered in steel now, and since Factorissimo buildings have finite floor space, it freezes up looking for a free spot to drop the item. When I delete it the game runs smooth again.

I guess ideally I would add some kind of alert that disables the thrower if that situation ever happens but I'm not sure how to do that atm lol

Oh no, damn. How did that happen. Thank you for investigating, I could not figure it out!

It's happened before lol, specifically with the factorissimo buildings. I'll figure something out one day hopefully