CZ3D has two modes one for old areas and one for new areas.....I really don't understand how they did it but the facets they fall in differ at times and most of your older nickels (buffalo, V. shield) read lower so in the advanced mode get an old nickel( one would not expect a newer nickel) should read nickel and in regular salt mode in newer areas new nickels should also read nickel.
Is there anything wrong with your machine (nope) is there anything wrong with your hunting choice of modes (yep) use the advanced mode for (older) areas and regular salt mode for newer areas.
I do realize if your hunting in an area that is a hundred years old and still being used you would have to make choice what to use depending if your looking for newer clad nickels or deeper
Buffalo, V, and shield. Also really deep Jefferson nickels may be a problem.
Your unit is working just like it should as thats the way it was programmed advanced(older areas) regular (newer areas) Hope this helps and do not compare a CZ3D with previous CZ's as its just a different animal..