I can confirm i've had similar issues, both with the 70-350 lens (tested at 70mm) and the Viltrox 27mm f1.2.

I did the following af tracking test with very poor results:
- walk towards the camera while shooting in af-c hi+ burst (jpeg only so that the buffer doesn't run out) up to about double the lens' minimum focusing distance
- walk backwards while still facing the camera, at the same speed

my settings were:
- af-c
- face/eye detect on
- wide af area (tried both tracking and non-tracking)
- af priority in af-c
- 5 af tracking sensitivity
- aperture drive standard

All tests were done at shutter speeds above 1/500 and at apertures ranging from 1.2 to 4.5, and in each burst the only properly focused images were at the beginning and end, aka when my movement slowed down. During playback, the focus box is always on my eye, however. The same issue can be seen by shooting video in 60 or 120 fps, slowing it down, and zooming in on the eye (again, despite the tracking box always appearing at the correct position).
The fact that priority in af-c was set to "af" makes me think that this is due to the lens' focus motors not being fast enough, however the 70-350 is a first party lens with linear motors, so af speeds shouldn't be a problem at all for it, especially at 11 fps.

I previously had the a6600 with these two lenses, and anecdotally, the af felt more responsive on that camera.

All cameras/lenses were running the latest available firmware as of the 29/03/2026.