Black spot on the wall like a shadow

Hello everybody.
I’m a new in UE. I was faced with a problem I can not solve it for a whole day.
There is a black spot on the wall like a shadow.
If I install Point Light, the spot will disappear and the wall will be clean, but it isn’t decision for me, mistake is obvious and I want to understand what it is.
Help me to understand.

Search this stuff it was posted many times here.