File naming

Hi -
I have a strange effect on my D3400:

I record in JGP/Fine & RAW which means that for each photo I get two files: DSC_1234.JPG, and DSC_1234.NEF

But once in a while, like once in a couple of hundred photos or so, the file names are NEF(1).JPG, NEF(1).NEF, and if that happens again NEF(2).JPG, NEF(2).NEF and so on.

By comparing the file-creation dates I find that those files seem to be not renamed to the DSC_.... naming convention because there is a gap in the sequence number.

I have a ScanDisk Extreme Class 10 64gb memory card, and the occurrence of this issue does not seem to be related to the speed in which I take photos (e.g. taking photos in rapid sequence).

Any idea where this could be coming from and how to avoid it?

The camera is brand new, less than 2 months old.

Thanks!

Are you seeing this on the memory card while still in the camera or on your computer afer you download the pics? If on the card, I have no idea. On the computer, the (1), (2), etc sounds like a windows thing, when you download the same file multiple times, you get a number.
If it is on the card, try formating the card in camera after you get all your pictures off. Many of us here format the card in camera every time we download pictures just for good luck.

It's on the memory card: I always leave the card in the Camera and download the files via the USB cable use the Explorer.
I run Win 10.

I can not explain it. Maybe formating the card will prevent it. I format the card to erase it every time I copy pictures. If you are copying via the usb cable, I don't think you can write back to the camera so it should not be an outside source causing it. I re-read your question and I better understand what you are saying. It sounds like the camera is doing it. If formatting in camera doesn't help, maybe ask Nikon about it.

I'll try formatting and see what happens...