My exterior mod centered in cell -2,6 has exterior navmesh complete, and performs as well as can be expected in a mod. All cell borders green, checks result in no errors, cover checked and finalized.

My Mod touches the following cells, and all show cell borders green, checks result in no errors, cover checked and finalized: priority navmesh to Labyrithian (Beth started but didn’t finish it to Whiterun road)(-3,7)// Main DovKroniid Redoubt fortification: (-2,7) north walls; (-3,6)city gates and priority navmesh; (-2,6) center of fortification and manor house;(-1,6) eastern towers; (-2,5) barbican; (-1,5)south edge of towers// Priority navmesh road to DovKroniid Advanced Camp: (-3,5); (-3,4); (-2,4); (-3,3)// DovKroniid Advanced Camp (-3,2)//Completed Priority navmesh road connecting to Whiterun road (-3,1).

When I load the mod I get bogus warnings about navmesh bounds in -3,6; -1,5; -3,2; -2,6; -2,7; -2,4; -2,5.
All of those except -2,4 have multi-story navmesh (stockade or imperial tower statics). At least that is all I can tell they have in common.

All of the above seems fine to me. I have patrol and adventurer and traveler mods and they are using the priority road from the Whiterun Road past my fortification (when I remember to open the city gates for them, lol) and through the Labyrinthian ruins. It is beautiful and immersive,

Now, here’s the problem. Initially the entire fortification and advanced camp are taken over by a faction of bandits lead by a boss calling himself, “the Bandit King.” In order to flank the advanced camp, it is desirable to travel from the Whiterun road bridge through cell -2,2 – which I have not modified.

However, just north of the little gully in that cell and around the ore site in a neighboring cell (-2,1) there is a CTD area that I cannot explain.

>>Any ideas on how to fix this or what would cause a CTD in a neighnoring vanilla cell?
Of note – if my mod is unchecked this area can be freely traversed w/o CTD.

Any ideas gang?
Question is: what would cause a repeatable ctd in vanilla cells near a modified one that tests out ok .

My guess is something you inadvertantly changed in the vanilla cell - I had this exact same thing happen to me with 2 different mods. One I managed to sort out (by going to the mod details and ignoring a list of things that I knew had nothing to do with my mod), however I still don't actually know what it was I changed in the vanilla cell. The second mod I still have no idea what I did, the only thing in the cell view window in that cell with an asterisk next to it (which I believe indicates I changed something) is the navmesh.
That one I have been unable to figure out so I basically canned the whole mod.

Thanks, Mohrdechaia.

The only thing I did that could affect the navmesh in that cell was finalizing the mesh in a nearby cell (which has to synch up with the vanilla cell's border.

I am mapping the anomaly. so far it seems centered on a star - navmesh (radiating out from a point). I will back up my current mod, and then try to renavmesh that area in the vanilla cell -2,2 to see if that does anything.

I will let you all know!