Nikon has posted this on their website:
Important
An issue has been identified in firmware versions 3.10 and 3.11 in which fine-tuning values selected for AF fine-tune > Saved value are not correctly applied when pictures are taken. A fix will be made available via the Download Center as it becomes available. We apologize for any inconvenience this may cause.
So, hold off on updating until it's fixed. Fortunately, this warning is on the firmware download page itself, however, if you downloaded the firmware and haven't installed yet, hang tight.
Important
An issue has been identified in firmware versions 3.10 and 3.11 in which fine-tuning values selected for AF fine-tune > Saved value are not correctly applied when pictures are taken. A fix will be made available via the Download Center as it becomes available. We apologize for any inconvenience this may cause.
So, hold off on updating until it's fixed. Fortunately, this warning is on the firmware download page itself, however, if you downloaded the firmware and haven't installed yet, hang tight.