Sometimes the third-party lenses struggle with proper functionality on a given Nikon camera. Or perhaps it's the other way around? We will never know for sure.
I have purchased a handful of Viltrox lenses for my Z cameras and they tend to work flawlessly,
except when Nikon has done a firmware upgrade. By default, I detect these anomalies when I'm far away from home and there is no opportunity of upgrading firmware of the lens(es) (Viltrox tends to publish firmware updates only days after Nikon has done their best to make the Viltrox lens unusable).
In this case I was shooting with the excellent Viltrox 75mm f/1.2 on my Z9. The 75mm is DX, but handles extremely well on the Z9, and the combination yields approx. 19MPix files, which suffice most requirements anyway. However, that day the lens wouldn't do AF at all. So I get a very blurred shot. Annoyed by this I fooled around with camera & lens, and thought I had sorted the issue. I might have had, but forgot the camera accidentally had been set to multiple exposures
After uttering a few well-chosen words culled from various Nordic languages, I returned home and did the Viltrox firmware update. No more problems.
Funny though I ended up keeping the two frames that had irked me so much. They are shown below.
