A new empire managed to spawn on my capital somehow, then another empire took all the rest of my sector capitals. One of my sector caps got re-designated as an imperial capital before being taken. The result was: I no longer had a capital, or any sector capitals, and thus no control any of my planets. Here's another thing: Two of the planets that were mine before, still displayed a large circle of influence (but this was fake influence as it didn't allow me to control planets around them). Also, I suddenly had an "Empire" tab on all my planets.
- However, this bug seemed to correct itself (unfortunately for me) when I re-took the sector capital that became my imperial capital. This caused the capital to go independent, resulting in the destruction of my empire. Watch TV says it also made my planets fail to display any overview after my empire's destruction.