HI!
If you use reveals where the door contour doesn’t match the opening like a Slanted Reveal, the black dot will appear. If the wall opening is simple, the points of the door and the points of the wall’s hole are covering each other.
Please go to Door Selection Settings (Ctrl+t) > Hinged Door Settings > Wall Opening > Reveal and adjust your settings there.
Choose a different type of reveal and you will be able to see those points independently. See image