Without seeing the model it is very difficult to diagnose.
Have you got a section cut here?
Yes I use section cut here
Do you have all the raw geometry correctly grouped and the faces correctly oriented (white facing outwards)?
Turning “use object material” option off in Vray geometry, section plane settings may help..
If you have the section cut on the same plane as a wall - it can create z-fighting like effect and cause things like this.
Try moving the section plane a little bit away from any surfaces in your model