I was wondering the same.
Sigma and Nikon seem locked in an arms war, with Nikon’s camera firmware updates crippling Sigma lenses’ AF, and Sigma’s lens firmware updates undoing the sabotage.
See here if this is news to you:
http://www.dpreview.com/news/2013/11/19/sigma-issues-advisory-on-lens-compatibility-with-nikon-d5300
The Nikon updates have also blocked use of 3rd-party batteries. Pure hostility toward the end user.
I respect Nikon’s heritage and technical prowess, but their recent contempt for their own paying customers is despicable.
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.