Ian I think you should be able to replicate what I did by following these instructions (if you want to). The key seems to be cleaning up the mesh in one specific area, it is possible you could clean it up in any way you wish to, but it might be safer(?) to follow what I did, I tried the exact thing twice with a complete redo in between with same successful result, recording what I did the second time. I didnt bother cleaning up the seam blends after myself, so I know it doesnt look beautiful after my last step, but I didnt see the point of doing anything more myself after that point - I dont even have your most recent version, and Im thinking you could clean up by repairing the one seamblend between the light-brown and darker brown textures without risk of making the glitches return, as long as you keep it simple (though honestly, the area isnt seen during normal play except for on the top cam, so if you wanted you could just plant some trees to cover the top cam and be done with it). If you decide to clean it up, probably best to make a save in between and doublecheck that it gets rid of the glitches for you as well.
1. The picture below shows what I identified as the "problem area", I marked with red the specific area that I suspect is the main problem, with the yellow markings possibly mattering too. (The purple marks one large face, which I destructively deleted during my earlier test - along with the one face closest to it in the red-marked area - with the result of eliminating the glitch for me. But nevermind that, it doesnt seem necessary to delete any faces)
- U1.jpg (444.72 KiB) Viewed 3569 times
2. The picture below shows how I select faces with the box select tool (I hold shift down for the second select). It is important to use box select in order to make sure all the razor-thin faces get included in the selection. Dont miss the 2nd box select depicted on the right.
- U2.jpg (510.3 KiB) Viewed 3569 times
3. I turned all those faces into the light-brown Rough texture (this makes verts in the area less reluctant to being deleted), in the picture below on the left you can see the selection having changed texture. I apply your usual planar mapping meant for this texture because why not. Then on on the right I have box selected those verts. Notice that it says 15 verts selected, which means there are 9 of them within the green circle I drew.
- U3.jpg (480.48 KiB) Viewed 3569 times
4. I press delete verts. only 2 refused to be deleted, that seems fine to me. Result seen in picture below on the left. You can also see the small red circle of the Terrain Painter as I am in the process of adding just one vert there with the painter (remember to have the correct settings and check that only one vert gets added). This might not be necessary but I did it as a quick and simple way of automatically turning edges in the area into neater positions. Result on the right.
- U4.jpg (496.68 KiB) Viewed 3569 times
Then I did V&S, checked in game and glitches are gone for me, I tried my best to check many angles and they seem to be all gone. Again, the area isnt left pretty, but you should be able to repair the light-brown to dark-brown seamblend if you wished to, I doubt it risks getting the glitches back unless maybe you add a ton of verts or something. And again, you could just plant some trees over it and no one's going to see it anyway.
I had many motivating factors to try figure this out, not least the fact that the real course Im working on - being a mountain course - has a ton of water with lower terrain nearby so I've long prepared for possibly being forced to deal with issues like these. Just look at this hole for an example...
