[sandworm]

Imho this might be an orbital adjustment tool.

The thing has solar panels and is in a low orbit. So those panels are a significant source of drag. Normally this is a problem, but perhaps they are using this drag to adjust the orbit. I'm not talking plane change. I mean controlling the amount of drag to adjust orbital speed/altitude/period.

Even with all their extra fuel, spy sats do not make plane changes. A significant change would require hundreds of m/s and they have, at best, 1000m/s for their lifetime. (Xenon is power-hungry/tricky/slow and therefore not suitable for quick plane changes). These are multi-billion dollar assets with lifetimes measured in decades. You aren't going to spend 100m/s and shorten the lifetime of the asset by years, effectively spending a billion or more, on a plane change.

What they might do is adjust the timing of flyovers by controlled changes to orbital periods. Rotating solar panels, a significant source of drag and reflection, could give some control. Such a maneuver would probably be done at the lowest point in the orbit (highest drag) and could explain the quick and apparently random change in reflectivity.

The test for my theory: Does this disappearing trick happen more often at the low point of the orbit? (If you call that the periapsis we know you spend weekends on Duna.)