Yesterday I had an issue with my D500 AF. First the AF-ON button stopped working, then it started working but the rear toggle stopped activating AF. Finally I bit the bullet and reset my camera and that fixed the issues (for now), then I spent some time restoring the camera settings to the way I had them. Maybe I should have saved the camera settings before hitting reset, but then maybe the problem I was having was baked into the settings at that time. The point is that it's a good idea to save your camera settings right after they are configured and saving that file on a memory card or on your computer. Lots of you will say "duh," but I've had this capability dating back to 2005 with the D200 and have never had it be an issue until yesterday.