From Nikon:
Thank you for choosing Nikon for your photographic needs.
We have received indications from some users that when photographing scenes in which an extremely bright light source, such as the sun or high-intensity lighting, is at a certain position along the top border of the frame, flare with an unnatural shape caused by the reflection of the light may sometimes occur in images captured with the D750 digital SLR camera.
As we at Nikon are constantly striving to ensure the satisfaction of our customers, we have released this announcement to inform users that we are already working on measures to address this issue and will, of course, keep you advised of these as they occur.
Please direct inquiries regarding this matter, contact Nikon Customer Relations by phone at 1-800-Nikon US (1-800-645-6687), 9AM–8PM EST, Monday to Friday (closed certain holidays) or online here.
Once again, thank you for choosing Nikon for your photographic needs.