It should recognize them. It's not normal. Is it still the same after a restart?
I had the same problem (intermittent) and ended up getting a SanDisc USB3 card reader and transfer speeds were a lot faster as a bonus. Besides this way I am not plugging in the D800 over and over and physically stressing that port on the camera all the time expediting wear and tear. The fastest USB3 card reader right now is QUITE affordable too :-)
Is this the first time you’ve tried LR with the photos, or did they work in LR 5.4, but not LR 5.5?
The D800 should be recognized just fine by LR; however, if the photos are not, then what probably happened is you’ve used an older Nikon program to transfer or view the files, which changes something in each one and makes the unrecognizable to Adobe products.
You can update your Nikon programs to ones that are as new as your camera, or stop using them altogether.
To correct the issue with the current image use the following utility:
I've just downloaded new photos from Camera Nikon D800, they haven't gone through the Nikon program and have had no problems
Thank you !!!!