Just to say, latest update I started a new game and revisited the area, no problems at all, nice one!
I have updated gxf drivers since, if that makes a difference
Initialize engine version: 5.5.2f1 (5e0c7f8a0b57)
GfxDevice: creating device client; threaded=1
Version: Direct3D 11.0 [level 11.1]
Renderer: NVIDIA GeForce GTX 960 (ID=0x1401)
VRAM: 2016 MB