I get same thing only I can move through Morthal a little bit before I CTD, swamp and western shoreline is instant CTD, only mods I can think of that would affect Morthal are Expanded Towns and Cities, Realistic Lighting, Improved Interior Lighting, W.A.T.E.R., SkyTest just Animal Behaviour, GetSnowy and Immersive Travelers. I have made new games without some of these mods installed and I still get CTD. Can you post any mods you think may affect those cells so we can compare?