It's a real stretch to say there are AF Tracking problems with the D850. Yes - the D5 may have faster response and slightly better AF performance, but the D850 matches or exceeds the performance of the D500 and probably any other camera on the market.
I just finished a week with a wide range of photography from polo matches to professional golf. The D850 performed wonderfully for polo in a wide range of changing conditions. For golf, it rendered images with great color straight out of the camera. The percentage of keepers was better than expected. In the test posted above, while 3D is one option, Group AF would have eliminated virtually all the out of focus images. There is certainly a difference comparing the D850 and D5, but why compare photos using the wrong AF Area Mode for the job? You have an erratically moving subject so 9 Point Dynamic, 25 Point Dynamic, and Group would all be better choices than 3D.