Back up just a touch and re-shoot the photos. When you are REALLY close and wide open, even small vibrations or the floorboard moving as you change your weight from one foot to the other can have an effect on the photo. I know it sounds wierd, but at f/1.7, the depth of field is quite shallow...within a few millimeters...when you are at minimum focus. Also, when I first began trying this myself, I found that all of my 50/1.7 lenses had a bit of back-focus. I later found that the older lenses all had a bit of focus issues. Newer "made for digital" lenses showed less of this. My newer 50/1.4 RS had no problems, and my 100 macro RS had no problems either, but the beercans did. This is really only noticeable wide open and close to the subject, but it is frustrating!
Is each lens different, or do they all display the same amount of focus issues? Remember that the center battery should be clear right at the front, the front battery should be most out of focus and the rear battery should be somewhere in between.
Also, remember that a longer focal length will show more drastic results.
Here is one I took a few months ago when I first bought the 24-70 Z SSM. This is also at 50mm, but it is f/2.8 (wide open). This is the way the results should be...center spot on, rear is a bit out of focus, front is more out of focus.