Nikon D800 and CF cards

I like to share a recent experience. I typically filled the two card slots of my D800 with one SD and one CF card, CF being the second and set to take the ovweflow. I paniked when I was missing some shots from an important shoot on the SD card;I could see the images in the camera replay but not on the SD card. When I just left the CF card in the camera, the images where clearly there but, I don't own a CF card®eader and the USB wire connection did not work at first. only after using Adobe Bridge, I was able to down load the image files.weird. any explanations?

similar here, with D810 I shoot jpeg on SD and raw on CF, once my CF cardreader stopped working and so I transfered images via USB from cam to win10 pc using explorer.
Jpegs from the SD card worked well, but that raws from CF card run crazy, after 1 or 2 files the next file shows as a about 500MB file on harddisk and explorer freezes. Tried it with 4 different CF cards to make sure it is not a card failure.
Regards
Martin

With the D800, and probably many two-slot Nikon cameras in overflow mode, when the camera is clearing the buffer, if it calculates that the first card will fill up, it will start writing to the second card. When the buffer is clear, if there is actually still more room on the first card, it will continue writing to that one- so you can have images written to the second card essentially "out of sequence," like you're describing.