Nikon has released a D850 Firmware Update. It deals with these issues:
• Fixed the following issues:
– Users exiting Clean image sensor after adding it to and entering via MY MENU would be returned not to MY MENU but to the SETUP MENU.
– Photos taken with On selected for Long exposure NR would sometimes have increased noise or shadows with a greenish cast.
– Slight aperture reset lag would sometimes occur after shooting at shutter speeds under 1/10 s (type E and PC-E lenses excluded).