Hello!
I noticed something odd:
I added in my scene a Skybox with Scene Texture using a Scene Capture Cube, and it seems that all my translucent and additive materials are not rendered / occluded by it when they are in front of it. Is that a problem of render priority? I use Forward Rendering
Does somebody here knows what is going on? Is there a solution to this problem?
Thank you! 
PS: Here is the problem, the pink cube is translucent and occluded by the skybox (dark green)
