I saw the exact same case a while back on the Discord server. But its most likely a issue with the SOI.
I have a few questions so i can make a accurate conclusion:
- Is Numachi orbiting outside your star's SOI? (Show a screenshot of its orbit compared to Zeus's SOI)
- Had you tried restarting your game while inside Numachi's SOI? (Try fully closing the game, then open the game again, then switch back to your spacecraft inside Numachi's SOI)
- Could you show us the OrbitData part of Numachi's and Zeus's planet files? (If the values are negative, It can break the planet and/or star)