What's causing bruising from filler after 4 months? (Photo)

I did a subcision at my cheeks to try to release some dimpling threads and a week later, even though the bruising minimized but not totally gone, the doc recommended a cheek filler on top of the bruised area as the dimpling didnt go away. 4 months later, the bruise/ brown/greyish color is still there. What could the cause of this be?