I'm posting an update.
I've not been through four copies of the sigma 50 art. All of them have focus problems.
#1, #3, and #4 have the outer point front focusing problem. Center point is fine, most of the time, though they do randomly miss occasionally, but whatever.
#2 seemed to not have this issue, but I returned it because I found a better price elsewhere (it was bought at an inflated price due to supply and demand). It also, may have had the issue, and I just didn't notice or was in denial because I didn't want to return another one over that.
I did use that one at a wedding, and after going through the photos I noticed that the in focus percentage was extremely low, say, 30-40%. ESPECIALLY with servo focusing.
So, here I am, I have two copies sitting at my house waiting to be returned to the dealers who sold them to me. I feel horrible for making so many returns, and I'm getting tired of playing this game. But they just plain, do not work right. Tested on three camera bodies that have no issues with other lenses.
SIgma service has acknowledged that this issue has been reported by some people, but that there is no way to fix it yet. They are waiting for the company to release new firmware and software that will allow them to fix this.
I have also read in other forums of many other people having this exact same issue, so I know I'm not crazy, and it feels better that I'm not alone. This lens is such a tease. Incredible optics that you can't make use of because you can't trust it to focus properly.
2x Nikon D750// nikkor 24-70 2.8g // sigma 35mm 1.4 art// sigma 50mm 1.4 art// nikkor 85mm 1.4g// Nikkor 70-200 2.8 vr ii // 4x SB700// WL x3200 + x1600 http://www.marekkphotography.com