I don't know what it is but it feels like i went from crashing like maybe once a week, to multiple times a day as time has gone on.
Make sure to disable all autosaves, disable quicksaves, and never save over an existing save. Something about Bethesda's save system has never quite worked properly when overwriting existing saves (which is how autosave and quicksave function), you have to force it to create new saves and manually delete the old ones yourself later.
After the remaster came out, I started replaying the original with a small modlist, and saw similar degradation in stability until I remembered to do that. Currently it'll crash if I've had the game open more than a couple of hours, so I just manually save often and restart the game any time I feel like it's been open for a while. It doesn't seem to be getting worse anymore so I think I'm in the clear.