I don't know if it's just me, but I'm fairly sure I've seen others complaining about this stuff as well. Basically I have a tendency to get a high amount of CTDs or freezing whenever I'm playing with mods that alter Skyrim's existing worldspace extensively. This can be something like the Fight Against the Thalmor quest mods, which add numerous buildings and dungeon entrances throughou the world, or the most recent Immersive Settlements which expand all the town areas. No idea why this is happening, and it just feel so damn unfortunate since it makes me extremly reluctant to install any mods that alter the vanilla worldspace, not to mention I feel very creatively restricted when creating my own mods since I want them to cause as few problems as possible.

I hope someone out there has some insight on what causes this stuff and if there is any way to fix/minimize it.

I believe it has a lot to do with the navmesh management. Vanilla ones are... easy to break. Could be other things, but that's usually the "go to guy" when things error away with exterior add-ons.

Sadly vanilla ones need to be altered if any objects, especially buildings, are added, no way around it. Personally I have yet to experience a CTD from heavily altered navmesh, but it is buggy as hell sometimes for no apparent reason. :/

Yeah but there are rules to follow when needing to edit a vanilla navmesh in specific ways. There are certain things you cannot do with vanilla navmeshes.

What exactly are you not supposed to do with them?