It does it with or without Vulkan I'm afraid. It is almost like something to do with the loading of the clouds as you get closer, changing perhaps from one type to another(?), for example as I was taking off, they were all fine, even the ones ahead (I was some way off them) then I looked to my left and just noticed one cloud starting to go funny, I moved my head from side to side slightly and it was changing in kind of layers, then as I went along a bit more, it sort of loaded and sorted itself out, then the ones in front started to do the same thing etc. I don't know how this is done technically or that helps shed further clues on it. Of course if you can't see this at all, there are many factors with VR / many backend settings it could also be. As I think I first mentioned, I never had this issue for a long time prior and I've been progressing with VR for must be a year now. So certainly a earlier version of SkyMax did not have this issue with VR - I'm just not sure at what point it happened, was probably near the Vulkan release which confused things a bit.