D800 focusing to minimum?

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Hi everyone, I have this very annoying issue. Recently, when using the AF, in all modes, my D800 struggles to focus to objects far away or with low contras, or actuslly anything sometimes. All that happens is the lenses zoom to their minimum. No hunting, no going back and forth, just around to the closest focus they can at full speed (quick on the 24-70!)

All lenses seem to be doing this, my most common lenses, the Nikon 24-70 f/2.8G and Sigma 150-600 C both do the exact same thing, which makes me think it's body related. The sigma will even bust through its 10m focus limit right down to the closest it'll go even though it's restricted it.

I always assumed if a camera cannot focus, it will go to infinity, but mine seems to go the other way.

Any reason this would happen? There is quite a lot of dust when looking through the viewfinder, but the sensor is clean. Perhaps some dust on the focusing system screwing it around?

Any ideas where to start would be greatly appreciated.