Since free oxygen is about 0.1 parts per million in Venus' atmosphere, an infinitesimal fraction of the amount on Earth, the intensity only confounds the puzzle. One other feature of the data is that the oxygen is strongest in the center of the disk, and drops away as the data nears the limb. On Earth the atomic oxygen is created from carbon dioxide on the dayside and moved around by the ionosphere. On the night side the atoms recombine to form O2 and ozone, among other molecules. While Venus also has an ionosphere, its lack of a magnetic field means that the ionosphere doesn't operate as smoothly as on Earth.
Particles tend to swirl around and flow in a disordered way.
Granted that PVO and Venera were examining Venus during a solar minimum and we are now at the peak of the solar activity cycle. Maybe the atomic oxygen generation is affected by the solar cycle. That's one possibility, but the lack of a magnetic field problem makes that unlikely. Something weird is going on in the upper atmosphere of Venus. The first bottom line is that we just don't know what's going on.