Possible focus bug with A7RVI and 400-800mm

Hey!

After a few months of testing out my new A7RVI for wildlife, I noticed a peculiar behavior with the A7RVI and the 400-800mm. I would like to know if anyone else has noticed a similar issue:

When using the 400-800mm, using "AF tracking sensitivity for speed change" on either -1 (stable) or +1 (responsive) makes the AF very unreliable, even on static subjects. The AF keeps focusing back and forth. This seems to be amplified when "AF lvl for crossing" is set to lower values like 1. When setting tracking sensitivity to 0 (standard) and AF lvl for crossing to 5 (Responsive) the camera performs basically flawlessly.

This issue did not happen with the A7V I used before I got the RVI. I used the same 400-800mm with the A7V and it worked flawlessly no matter the AF settings.

I am just wondering if maybe this is a firmware bug between the 400-800 and RVI since the issue does not happen with a third party lower focal length lens on the RVI.

It's not a huge issue for me since the camera can track swallows coming towards me very well even with AF sens. speed change set to standard, but I would of course like to get that extra bit of responsiveness that the camera offers on that setting.