Nikon today released firmware version C1.10 for the D810. The update contains one new feature—the ability to control Atomos-compatible external video recorders from the camera—as well as 14 additional bug fixes and clarifications. Many of the concern Live View and video recording, plus one problem a number of people have reported concerning the camera incorrectly assigning file numbers has been fixed.
All Nikon firmware updates are now centrally served from nikonimglib.com. The D810 update is here. But while you’re there, you should check to make sure you have the latest Distortion Control Data, too (L2.009). As I write this, the D810A has not had a firmware update, but you can check here for the latest information.