There is no systemic or systematic problem with Nikon autofocus. On the contrary. Very likely it is the best on the planet, in capable hands. I have used Nikon AF since 1989 Nikon F4. It had the very lowly (by today's standards) AM200 autofocus module. Even a current D3400 runs rings around that professional body if we only compare AF capabilities.
Occasionally there might be a broken lens or a broken body, that's normal for any manufactured goods, but that's why the buyer is protected by a warranty.
Autofocus is not foolproof, but the caveats are listed in the user manual. Strong contrast or complete lack of contrast or strongly coloured light can cause AF problems, but there's workarounds and in the extreme case there's manual focus. In the end: It doesn't matter what gear you shoot or how you shoot, just get the shot.
Using AF to the fullest is a skill and needs practice. With almost 3 decades worth of experience with Nikon AF from F4, F5, F100, all D1, all D2, all D3 and all D4 models and about two dozen others including my daughter's D40, I feel I am qualified to say that if one cannot get a sharp image with a Nikon autofocus camera, the problem is definitely not the camera.