Black box in the center when exporting

i got an image with a small black box flashing on and off.
i find there's a node using window (doing vignette thing), and in the highlight parameter i might touch the mini panel by mistake so it's -0.02, very very tiny so it might be the reason. after I change it to 0, black box is gone.
i find there's a node using window (doing vignette thing), and in the highlight parameter i might touch the mini panel by mistake so it's -0.02, very very tiny so it might be the reason. after I change it to 0, black box is gone.