Troubleshot the issue in Discord. Combat Robots Overhaul is the culprit. Disabled it and I had no problem trimming the surface.

I loaded your savefile with a small subset of your mods (SE and its dependencies + K2), and I was able to trim Nauvis in about 30 seconds on a laptop. One of your other mods (which I didn't have enabled) is presumably listening for chunks getting deleted (or registered entities getting destroyed) a...

I waited probably at most 20 minutes. I tried both SE's built in trim and the mod "Delete Empty Chunks" and they both do the same thing. I just tried /editor mode. It won't let me delete surface. "Remove empty chunks" does nothing. I'll try trimming it over night and see how it g...

Someone let the surface scanning go wild and blew up the size of the save file. Trying to trim it to upload it to Factorio.zone but it seems to get stuck after figuring out which chunks to delete. The issue might be similar to the one in this thread but I don't have fCPU: https://forums.factorio.com...