Some objects not affected by post processing?

I have a material set up that I have added to the array of Rendering Features, what this material/post processing effect does is that it adds an outline to objects. However, only some are effected. For example as seen in the image below, the carton of milk is affected, but the ball (which is the player BP) is not. I have ‘Render CustomDepth Pass’ ticked on both the carton of milk and the PlayerBP, yet only the milk carton seems to be affected. The ball itself is slightly transparent, could this be the problem? Any help would be greatly appreciated.