I found 3D to want to jump around way too much. I would prefer the system to continue to track what it started on until I let off the AF button or I tell it to switch subjects with the little arrows it sometimes brings up. I understand that there will be more complex situations where any tracking system will get confused and jump to other things but Nikon's 3D is jumping way too often and in situations where it really isn't confusing at all. I had 3D on a kingfisher that was perched out on the very end of a long branch. So nothing else around it. Background was at least 1000 feet away and grossly OOF...the 3D thing would all of a sudden jump down the perch which looked nothing like the kingfisher and it would also all of a sudden drive focus all the way to that distant background. This was with a Lock on of 5. Even in other modes like Wide-Area I would aim it at the duck I wanted, it would see the eye, start tracking the eye no problem. Then for no reason jump the eye to another duck nearby. This was one of my big AF complaints when using the Z9, lack of persistence. Aim the A1 at your subject and the thing will ignore everything else no matter what is going on. I had both cameras out going back and forth between them during my testing and it was quite striking the difference in behavior.
...and [3D-tracking] blocked shot AF Response is mode [3] only.