Post Process Material wont render on certain areas.

Hi, so as the title says. I have a post process volume in my level. I use this to trigger outlines on different actors within the scene when the mouse hovers over them. It was working fine but I realised when working on another area of the level that the the outline would not show. This happens using the exact same actors so I’m not sure where the problem is. Is there something about post process volumes that i’m missing?. I’ve also tried placing another post process volume in the level with the same rendering feature but it still doesn’t work.