In June 2014 discussion at the old BethSoft forum, after months of effort, developing 2 scripts that are now distributed with xedit, I'd submitted a navmesh patch fixing every triangle missing its "found" flag. I'd thought my patch had been incorporated nearly a decade ago. Now, I've discovered that at least some of it wasn't integrated, or was subsequently lost.
Unfortunately, that is for oldrim, so I'll probably have to re-create them for SE. I've not figured out how to tell SSEEdit to copy worldspace blocks of an old version into a new SE version.
This patch allows the NPC follower to walk with you from the North entrance to Labyrinthian.
One significant issue is there are many missing preferred flags on tiny sliver-sized triangles, making the preferred path useless. Some of the vertices are so far off the ground that NPCs cannot use them. There's a narrow hole (missing triangle) in the middle of a stair. And there are triangles that climb rock faces and ledges.
The SE CK reports:
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 262 and 379 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 262 Edge 1 and Triangle 379 Edge 1 should be linked, but they are not.
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 375 and 379 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 375 Edge 1 and Triangle 379 Edge 2 should be linked, but they are not.
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 377 and 379 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 377 Edge 0 and Triangle 379 Edge 0 should be linked, but they are not.
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 and 262 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 Edge 0 and Triangle 262 Edge 2 should be linked, but they are not.
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 and 375 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 Edge 1 and Triangle 375 Edge 2 should be linked, but they are not.
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 and 377 have opposite normals but are linked
Navmesh 000d698a Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C), Triangle 379 Edge 2 and Triangle 377 Edge 1 should be linked, but they are not.
NavMesh: Navmesh (000D698A) in Cell NavMesh (000D698A) with 385 Triangles in Cell 'LabyrinthianExterior03' (0000945F) (-6, 10) in WorldSpace 'Tamriel' (0000003C) has warnings that need to be fixed
Causing missing found flags on:
Triangle #142 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #292 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #366 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #367 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #369 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #372 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #373 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #374 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #375 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #376 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #377 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #378 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #379 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #380 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #381 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #382 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #383 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))
Triangle #384 in [NAVM:000D698A] (in GRUP Cell Temporary Children of LabyrinthianExterior03 [CELL:0000945F] (in Tamriel "Skyrim" [WRLD:0000003C] at -6,10))

Attached Files:
labyrinthian exterior navmesh.7z