There seems to be an issue with video stabilization in 8k. If you have video stabilization on when recording in 8k, the stabilization seems to "fight" the panning movement of the camera. You can confirm this by panning between two objects (while recording in 8k), centering them on each object on the screen. If you look at the recorded 8k video, the camera hardly pans at all, making you completely miss your subject, especially when zoomed in. Seems the 8k camera is not doing the same thing as the camera that displays the live view on screen.
Solution (at least until Samsung fixes it) is to turn off video stabilization when recording in 8k.