Terrain Bug ? at 18 seconds if you want to skip to it. Its like Mesh has soft spot

After the truck sinks into a mysterious hidden hole or soft sport, Rebuilding collision did not do anything. Running the Visual Debug in this video too, no static or holes from what I can see on terrain. I know I had a track there at one time but deleted it to make sure and rebuilt collisions in edit. Turned on wireframe too in this video if maybe someone can spot something I am missing. I can just put a mesh road over that spot and give a thin thickness, and hide it to more less put a band-aid on this spot. Really curious if this happened to anyone else. Only time I seen something like this happen is when I made the break angle of a mesh track .15 or less, I started falling through the mesh even after rebuilding or getting flat tires. I suspect somewhere in the actual file of the terrain where all the info is stored, there is residual data from something deleted. Was not sure if deleting something in the temp folder would correct it. Know it makes some CDAEs for models, not sure about Terrain Blocks. I should say, this is the Grid Map terrain block modified. It may be a locked something that is similar to the trees below it I can not delete.
Thanks A lot if anyone can solve the mystery or tell me what caused it.
Not the crash at the end. That is not a issue.
Unknown Terrain Bug - Soft Spot on Mesh ? - YouTube