This sounds like the same problem I had. In your Octane Render pane, under System, what're your texture counts like? I found my materials would "disappear" (go grayscale) randomly when I had passed over the RGB texture limit for CUDA.

Reality and 3Delight don't use CUDA so they don't have the same ...

An object that is flagged as visible(or visible in render depending on setting used)will have the textures defined in its octane materials count towards the cuda limit.

Objects Deleted or flagged as not visible will not have its textures in gpu memory.

This indeed seems to be the case! At least ...

I'm having a bizarre issue with one of my scenes. I was using the clean police car from Stonemason's city ruins, and the texture randomly lost all of its color on the car (in fact, all the textures/materials attached to the car had the same problem.) I manually deleted all the materials and ...