Sounds like you assigned a preset to be assigned to all imports from that camera.
Check the settings in the "preset" tab of the "preferences" dialog, although it sounds like you already did that.
In Develop Module (a Nikon D610 image selected)-
In Camera Calibration- Set "Profile" to Adobe Standard.
On the menu "Develop", choose "Set Default Settings".
This is a setting (NOT a preset) that will apply rendering 'adjustments' when images are imported. Lightroom has to have some guidance as to how it renders RAW image data. Or you may prefer to accept Nikon's "Camera Vivid" as your import default!
Thanks for the feedback.
It seems I solved the issue by going into the prefreneces menu and in the presets tab, I clicked the "Reset all default Develop settings" and this has cured the issue. Images are imported and processed into flat, un-edited RAW files.
Again, thanks for the help.