I've updated firmware for my Nikon D5300 earlier... Is it normal that the autofocus on my Sigma lenses stops working after updating new firmware?
Firmware updates for camera bodies (Nikon, Canon, Pentax, Sony, and others) sometimes disrupt compatibility with 3rd party lenses. Sigma is likely to produce a firmware update for recent lenses. Older lenses are less likely to have an update available.
You may use the Sigma USB Dock to apply firmware updates if your lens is part of the Global Vision Series (Art, Sports, or Contemporary). If your lens is not compatible with the USB Dock, it may be updated by an authorized Sigma Service Center. Sigma often makes such updates for recent models available at no charge, but the owner of the lens is responsible for the shipping costs.
I had the same problem with my Nikon D7100. After updating to the latest firmware none of my Sigma lenses would autofocus. After much research I read that downgrading the firmware was virtually impossible. I thought what the heck, I had nothing to lose. So I trawled the web and found the last known firmware before I had expensive Sigma doorstops and plunged in to downgrade the firmware. SUCCESS!! I now have all my Sigma lenses back. I will do my research next time before upgrading.
Had the same problem with D7100 c1.04 firmware. Luckily I had 1.03 binary file still on my computer. Everyone said that downgrading isn't possible, but I had no problem whatsoever.
No matter what kind of electronic device is in hand, don't fix it if it aint broken. Apply firmware updates only if you have some kind of issues and update has a fix for it...