I was recently shooting my daughters softball game with my D810. I shot for over an hour with no problems. However, once my daughter was put in to pitch I immediately noticed what appeared to be exposure bracketing as every 3 images appeared to have different settings. I quickly confirmed bracketing was not on and saw that the camera still said all the photos were taken with the exact same settings. I shoot everything on all Manual settings ie. Aperture, Shutter, ISO, WB, so I'm very confused on what could have caused this.
I also thought it could be something to do with the White Balance however this was set manually at 4550k. Furthermore, these are shot in RAW and the darker images are definitely grainier with more information lost similar to being underexposed. I have been shooting Nikon DSLRs as an amateur and now professionally for almost 15 years. I have never had this happen with one of my cameras. I shoot Commercial/Advertising for a large corporation but love to shoot my daughters sports in my off time. Has anyone had a similar experience? I have attached some images. Thanks!