The autofocus of the lens does not work correctly and / or does not work stably with individual specific cameras (in my case, this is a Canon 70D). This is expressed in "walking" autofocus, other things being equal, shooting conditions, even if they are good: from a series of shots of the same object, many frames will be with front or back focus. And this is not at all "not hitting the depth of field at aperture 1.4", "crooked hands", etc., as individuals explain.
Since the official Sigma service center is currently only in Hong Kong, and I'm from another city, I don't know how it is possible to fix the problem by adjusting the lens to the user's camera. I called the SC for advice, tk. it was too late to return the lens to the store and return the money. The specialist said that in my case, the adjustment most likely will not help, because. it is with the Canon 70D that they almost never succeed in making friends with this lens, and this is a compatibility problem, and not a defective lens or carcass. When asked whether self-alignment using the Sigma docking station would help, naturally, they answered that success was even less likely. I did not contact the Canon service center, because. they write a lot on the net about this - there is only one answer and it boils down to the fact that they are not responsible for the work of third-party lenses and cannot help in principle in any way (which is quite logical).
Despite the answer of the SC, I got a docking station and tried to adjust the autofocus myself. This is not an easy task and takes a lot of time (besides, there is no official method from the manufacturer how to do this), but I still managed to significantly reduce the problem with focusing accuracy by amending the autofocus operation for 4 different distances. The problem has not been completely fixed, so attempts will continue. Judging by the reviews, with some other cameras the problem is completely eliminated by both the docking station and the alignment in the SC.