Reliable AF in any light condition, not only the low one, is a combination of user skill and understanding, AF technology of camera and lens, and any possible misalignment of camera, lens, or user. No chain is stronger than the weakest link.
"Back (or front) focus" does occur, but perhaps far less frequent than most users tend to believe. One has to acknowledge that the camera's AF system has no understanding of "sharpness" in the way the human mind works, it can only maximise criteria of a given model. Thus, the camera cannot know that you intend only a small portion of the area covered by the AF sensor to be sharp ... so it maximises variance and puts the focus plane behind that small point because the entire AF-covered area according to its model now is "sharper". Just to take a common situation where we expect the camera to think like we do. It does not.
On a general yet related note, try working with AF *only* put to the AF-ON button of your camera. I prefer AF-C mode, but this has more a bearing on how you operate the AF-ON control thus any AF mode will work in practice. This approach provides much more control over what happens when you compose then push the release button.
