What you’re usually seeing first is the embedded JPEG preview, then the software switches to a full render of the actual RAW file.

Most RAW files (including Nikon NEF) contain a small JPEG that the camera creates using its own processing—things like contrast, saturation, white balance, and picture style. Cameras, phones, and editing apps often show that JPEG first because it loads quickly.

Once Lightroom or another app finishes rendering the RAW, it displays its own interpretation of the file, which can look less saturated or have different color balance than the embedded preview. The camera LCD also shows a JPEG-based preview, not a true RAW rendering.

So the difference is normal: fast preview JPEG first, then the final RAW render after processing.