This was cause by some post process not always sampling the highest mipmap. But if there is no need for mipmapping (i.e. no SSR) these levels will be undefined. So forcing all Post FX shader to sample level 0 fix this.
This was cause by some post process not always sampling the highest mipmap. But if there is no need for mipmapping (i.e. no SSR) these levels will be undefined. So forcing all Post FX shader to sample level 0 fix this.