Horrible AF Performance with Sigma 150 - 600 Sports and Sony a7r III

Allright, so I tested it out a little more in the garden.

With and without OS on a tripod. There were no problems with focusing at all in terms of sharpness, but sometimes the AF simply completely "broke", like when I was half pressing the shutter button and changing the subject, it stopped trying to focus at all and didn't focus anylonger until I fully pressed the shutter button to take a photo.

Also releasing the shutter button and re-pressing half for focus didn't work. This happened multiple times, so maybe this also happens when I'm shooting outside and I just didn't realize it until now (?)

And sometimes it just pumped liked crazy until it got back to focus anything (like 4-5 seconds or so). But I think this happened when I used the full range of focus and didn't switch to 0-10m focus distance, so I think this was normal.

Also I have to say that the AF-C didn't have a lot to do in a test-scenario like this, since I had no moving subject to test (so that AF-C would have to fine-adjust / fine re-focus again like in real life with animals). Very often the pictures are just slightly out of focus, when shooting in nature.

Except that the AF completely broke as described, it worked as intended as you would see in every test-video on Youtube (and as I would wish for in real life) when switching from subject to background and vice versa. But it's a complete different story when focusing on something that's moving (like the head of a deer, a bird or stuff like that). I don't mean crazy flying birds or running deer (I wouldn't even bother trying to photograph these with this lens) but standing deer that move their heads and look around.

No idea. I'm a little baffled to be honest.