Vray no longer rendering certain faces


So i have been having this problem crop up more and more and the last time it has happened it added at least 5 hours of work to fix the problem. Hope somebody can offer me some help.

So, i have been building the models as normal - ensuring as much as possible that the faces are forward facing etc. As i get towards the final stages with lighting and everything correct I will be doing multiple test renders and live renders. All that output correctly. Then potentially after I pick the model back up a day later, or as last night, set the computer to do some high resolution passes half of the model becomes invisible. Mostly single planes. But some elements such as glass suddenly has a second material in the back face (despite it not having anything other than glass on front and back faces).

This morning in order to fix it i have had to go into some of the materials and reflect then as there orientation had changed, some needed a simple inverted face, I had to add depth to some elements, remove depth from others. There seems to be varying solutions for different elements (glass for example, some had to be single faces, others could remain 10mm thick). Hence why it took hours to update the model.

What I don’t understand in particular is that this happens seemingly randomly, after multiple previous renders. The only thing i can think of that changed between the first renders and the second was I up’d the resolution and rendered with CUDA not just CPU.

Any advice would be much appreciated!
Thank you

If you want someone with knowledge of Vray to help (I don’t), you would need to upload your model and upload some screenshots of the Vray settings you use.
Otherwise people can only guess…

As much as possible is not good enough, they all have to be facing the right way…

The CPU and GPU rendering options (CUDA/RTX) are all different rendering engines, so the supported features of each varies.

It could be related to that.

When i say as much as possible, i mean everything that is relevant, the biggest issue is that fact that the faces for some reason switched without me doing anything.

1 Like

@tvooght :
SketchUp doesn’t randomly reverse faces without some user input, so I highly doubt that!
Maybe Vray does something like that, I don’t know…