1. Double faces. Delete those faces and check if there are more faces in that location. 2. It's just the viewport shadow. Switch to "Standard" shading from "High Quality" to see if it cleans up. 3. Viewport clipping / z-fighting. Your objects may be very large and close together. Turn off backface culling, and turn on Viewport clipping and tweak the sliders.
Replies
1. Double faces. Delete those faces and check if there are more faces in that location.
2. It's just the viewport shadow. Switch to "Standard" shading from "High Quality" to see if it cleans up.
3. Viewport clipping / z-fighting. Your objects may be very large and close together. Turn off backface culling, and turn on Viewport clipping and tweak the sliders.