I've had a strange issue with both my D700 and D800 that has been cropping up over the past 1-2 years, getting increasingly worse. It's a long story so I apologize for the length of this post!
Usually it starts after at least 100 frames or so, but sometimes I go through a shoot with no issues. I think mostly it happens when I'm using a flash on remote, although it might happen other times as well.
The problem is the camera won't shoot. The focus is set, no settings have changed from the previous shot, but I depress the button and nothing happens. Sometimes I can fix it by turning the camera off and on again, and sometimes I fix it by turning the camera off, taking the lens off slightly, and reattaching, then turning the camera back on. That usually takes care of it.
Given how I resolve it, I thought it was a lens mount issue. Initially it was only happening with my Sigma 70-200 which I've had for years and have shot A LOT with (I used to shoot sports). So I sent it in to Sigma and had the mount replaced and the lens serviced. While it was being repaired, I noticed it was happening with my Nikkor 28-70 as well. I've also shot a lot with my D700 (I shoot mostly weddings & portraits now), so I thought maybe it was the mounting connection on the D700. So I sent that into Nikon to have that replaced and the camera serviced. Note that I previously had both the camera and the lens cleaned and serviced locally prior to sending them in to see if that would work. So while my D700 was in the shop, I was using my D800 as my primary camera, and turns out it's now happening with that camera. So both my cameras and both my lenses, in all combinations are giving me this issue.
I've had the 70-200 and the 28-70 for somewhere in the range of 7-10 years and have never had these issues until the last year or two. And I bought both the D700 and D800 when they came out, so years apart. All were purchased new and I haven't had problems until more recently. Once it starts on a shoot, it keeps happening through the end of the shoot, which is highly embarrassing and very unprofessional. I change batteries, etc. and it still keeps happening.
Any ideas as to what is going on would be most appreciated!