Why does ambient occlusion make a black area above emission object? I did AO in compositor. The body of an emission object is invisible to the camera.
First screenshot - with TURNED ON AO
Second screenshot - with TURNED OFF AO
How it works and how i can keep AO turned on, but fix this problem?
Blender 2.91
You're using the image as a factor, so that heavily white area is getting AO applied to it with massive influence.  Use a viewer node to look at the output of your AO node.